Nevski,
As I've done a bit of research tonight I see that your sources have put it quite simplisitically. It appears that ROCOR was clearly in communion with the Serbian Church some time ago, but that they've drifted apart to some extent. Yet, the question of whether or not they are still in communion with one another seems to be disputed even today. I even found a few sources that indicated that ROCOR is even in communion with the EP. Can this be true? It may explain Elder Ephraim's history and current ministry under the EP, I'm not sure.
Much of the confusion here is a result of recent changes in the ROCOR's leadership/orientation. Put simply, ROCOR has been for at least a decade (though there are seeds of this much earlier) pursuing a path to place itself into the "mainstream" of what is often called "canonical Orthodoxy."
The confusion is, I think, symptomatic of a long term break down in discipline within the Synod, as well as some older issues which have combined to create much confusion.
For example, the issue of the Serbs: according to a fairly recent (and well known) communication between Patriarch Pavle and Alexis II/Agent Drozdov, Pavle repudiated his church's links to the ROCOR (this was, of course, before the recent open talks between the MP and ROCOR). Confusion is added, because it appears within the Serbian fold, you'll get different opinions - some bishops saying "ROCOR, a.o.k", others holding just as harsh a line as Pavle. Of course, it's also fair to say that Pavle's witness here is far from unambiguous - apparently he has had, at times, quite warm relations with ROCOR, been received as a Patriarch by ROCOR on a visit to the United States, etc.
The "Serb situation" is then further confused on the ROCOR side. If you ask most people (at least on the 'net, which is often not really representative on these things, I know), the Serbs and ROCOR are "in communion" - that concelebrations do continue between the two in many places, is well known. Yet even to this moment, you'll still find many (including a public statement which I believe was made by Bishop Gabriel, who is opposed to the negotiations with the MP) articulating the old line, that "no, we're not in communion with the Serbs". Part of the source of this confusion, has to do with the historical ties which have existed beween the ROCOR and the Serbs; I think it is fair to say that those who continue to speak of an existing communion between the two (all the while saying they're not in communion with the EP, or other groups over the issue of ecumenism), are putting sentimentality over good sense and canonical order.
A similar situation exists with the JP. It is only in recent times that the JP has been added to the limited list of those who the ROCOR (or at least many within her) claim to be in communion with. Historically, cordial relations exist with the JP due to the presence of ROCOR's mission in the Holy Land. However, I think it's far from unambiguous that the two were "constantly in communion", particularly given the perceived need by a delegation of ROCOR visiting the Holy Land, to squeeze a positive appraisal of the ROCOR from Patriarch Eirinaios. Also, I think it's extremly strange to speak of "communion" as well, given that in the United States, in some places, ROCORites are not supposed to go to the JP's missions in the U.S.
IOW, it's all over the place. Ecclessiastically speaking, it's incomprehensible, and the claims for "communion" or "not" become debatable.
The claim to "communion with the EP" is a very new one, and I think the most tenous. This is based on a recent concelebration in Europe, associated with the visit of a delegation bearing (I believe) the Kursk-Root Icon of the Theotokos; apparently it was an "on the spot" thing, and was (officially) not looked on well by Metropolitan Laurus. However, I'm unaware of anyone being disciplined in association with this.
What the ROCOR actually stands for on these issues, is hard to discipher. What is not, however, is it's official adoption (back 1994) of the ecclessiology of the "resistor synod" TOC ("Cyprianite" Old Calendarists) by the ROCOR - for the ROCOR declared upon entering ecclessiastical communion with them that they (Cyprianites) "hold the same ecclessiology which we do". While one could argue there is some ambiguity prior to this what the "official" ROCOR line in fact was on those they were not in communion with, this ended that ambiguity. Hence, what we can say, is that the ROCOR doese "officially" acknowledge that the grace of the mysteries does exist in "world Orthodoxy" (like the Cyprianites), that they are real parts of the "Orthodox Church", and not apostates/heretics/schismatics, etc.
Thus, ROCOR's alienation from them for several decades (which began in earnest after the EP "lifted" the anathemas the Orthodox Church had announced against Papism), is now "officially" acknowledged as being one only of "interuption in relations" due to some sticking points, and not the grave matter which was articulated in the 1983 "Anathema Against Ecumenism" which had been officially issued by the ROCOR and added to it's liturgical books for the Sunday of Orthodoxy (condeming ecumenism along with other heresies.)
Undoubtedly, it is this "at the top" recognition of the validity of the MP, and "world Orthodoxy" in general, which allowed for the more strident talk of "communion with the Serbs" and "communion with the JP" to flourish, and further, is what is allowing the current discussions with the MP to occur at all, with all of it's talk of "re-unification" and merger, rather than what should occur; a call by the ROCOR for an act of repentence to be submitted by the heirarchy of the MP, and talk of legitimizing them in the same way any other schism/heresy is reconciled to the Church.
As an aside, it was precisely the official adoption of the "Cyprian" position by the ROCOR, that led to the separation of a large part of it's presence in Russia to break with ROCOR, and re-form under the presidency of Metropolitan Valentin (of Suzdal) as the "ROAC" (Russian Orthodox Autonomous Church.)
But returning to the original point, it seems those two bishops you referenced really haven't rendered an accurate picture of the matter. So, let's just say that ROCOR at one point WAS in communion with the Serbian Church. Wouldn't that then have put it "in communion with" world Orthodoxy, in the same manner that the OCA's being in communion with Antioch allegedly puts it in communion with the Oriental Orthodox?
Two points...
historically, it cannot be said that ROCOR gets it's "legitimacy" from being "in communion with world Orthodoxy." This is not Orthodox ecclessiology - the Church "is", where a genuine Church is present... and this authenticity is ultimatly founded upon a true confession, and canonical foundation (and in that order; though neither can be ignored.) ROCOR, historically, had both. If it cut it's relations with every other "Orthodox" group on the planet, because of their involvement in ecumenism, this would not affect their own "legitimacy", since it would not be a schism, but separation from falsehood, which is not only "allowed" in Orthodoxy, but even required.
however, you do make a good point regarding the opinion that ROCOR is "in communion" with the Serbs and the JP. If this is in fact the case, then it is (at least in an ecclessiological sense) meaningless to say "otoh, we're not in communion with the Antiochians, EP, Romanians, GOA, OCA, etc.", since all this would signify (at best) is a break down in relations, and a sin on someone's part, against charity. While admittedly these things (even in times well before our own) can be messy, and remain ambiguous for a brief span (historically this was due to problems in communication), I think it's safe to say that this is not the situation we now face. Given this, I think you have a valid point.
Seraphim