Well, my dear Faldage, here is what I found at the Vatican:
1170 At the Council of Nicaea in 325, all the Churches agreed that Easter, the Christian Passover, should be celebrated on the Sunday following the first full moon (14 Nisan) after the vernal equinox. Because of the different methods of calculating the 14th day of the month of Nisan, the date of Easter in the Western and Eastern churches is not always the same. For this reason, the churches are currently seeking an agreement in order once again to celebrate the day of the Lord's Resurrection on a common date.
So I guess what you're referring to is the bit about calculating the 14th day of the month of Nisan. Although I also see what you're getting at. It would be nice to have some old calendars to peruse (rather than Googling, somehow this seems easier).
