You are making an assumption for which there is scant historical evidence one way or another. How do you *know* that the "original church" universally celebrated Passover always on Nisan 14 as the Jews did. We know that in the 150s or so, John's disciples did, and we know that Romans and everybody else did not. We don't know what the situation was in Rome previous to that--the Sunday feast may well go back to Peter. There isn't evidence one way or the other.
And yes, it caused a HUGH controversy, but the Quartodecimans did *not* call the Romans apostates or corrupters of Apostolic tradition. So I'm still not clear why *we* should call them that.
There significant biblical and historical evidence that the early church kept God's feast days, including Passover.
1. The only "official" scriputures they had were the books of the old testament. These books commanded them to observe the days God created, as they had been for centuries.
2. There is no indication that the incarnate Jesus Christ ever taught that observation of God's holy days, including Passover, were not to be done. In fact, Jesus Christ himself observed the days.
3. There is no indication in the new testatment that the early church stopped observing, or understood, that these holy days were not to be observed. To the contrary, there are numerous references to God's holy days, including Passover, in the new testament.
4. There is no controversy chronicled in the new testament having to do with changing the observance of these holy days. In contrast, the decision about whether or not gentiles were to be circumcised caused a (HUGH) controversy that was recorded and required a church council to decide. No such thing was done about whether to observe the days that God created holy and told his children to observe.
Putting all these together, it's not unreasonable to come to the conclusion that yes indeed, the early church did celebrate God's holy days, including Passover, and that later on this was changed.