Jean Serge
There are many examples of economia in history. The arians converted en masse to orthodoxy and the church could not baptise so many at once....so economia was used and they (who before did not belive even in the trinity) were accepted only by chrismation. But as St Nikodemus writes, a similar economia cannot be used to songle converts who should have the sacrament in the traditional, orthodox way. So, as I understand the example you gave, it was a question of economia. But now, when we can baptise propely and according to the orthodox intepretation of the canons, we have no excuses to baptise with sprinkling or just use chrismation. It is right that you cannot be baptised after you received the Holy Mystery of Chrismation, or any other sacrament. But here there is also different opinions.
Let me give you a example that I heard from a monk. There was a former catholic who converted in the ultra liberal Russian Church in Paris...parisjurisdiction under EP. He only confessed his sins and were received that way into the church. He tasted the mystery of Eucharist of course, but wasnt even chrismated. He then went to Jerusalem on a travel and told all this to a priestmonk who chrismated him. Then, on another trip to Athos he went to Esphigemenou monastery and they gave him baptism. So this individual converted three times to orthodoxy.
Personally I think he became orthodox at the second time. But if I were him, I could easily understand why he wanted baptism in the proper way. Now, it is not his fault or the more strict orthodox monks fault that they baptised him again. It is because this luke warm liberals that abuses the mysteries.