In Asia, Pascha was the observance of the Last Supper as a Christian passover, which sometimes included the slaughtering and eating of a lamb (cf. Aphrahat, Demonstratio 12, Epiphanius, Panarion 50.2-3, 70.12; cf. the later Byzantine-era description of Pascha in Walafrid Strabo, De Rebus Ecclesiasticus 18), and the Quartodeciman dispute was over whether the Holy Week fast (which varied in length from a few days to a fortnight, cf. the later fast of Lent) should end with Pascha or a feast on Easter Sunday (cf. Eusebius, Historia Ecclesiastica 5.23-25). The position that maintained that the fast should be broken on the day of the resurrection would preclude one from observing Pascha, and there were other reasons why Pascha was undesirable to some (e.g. it was viewed as Judaizing, cf. the anti-Jewish polemic in Melito of Sardis, Peri Pascha). The dispute did not concern whether the Eucharist (i.e. partaking the bread and wine) should be held only yearly on Nisan 14, as some have characterized it. The Eucharist was usually held weekly on Sunday (the Lord's Day), as Justin Martyr described it.
I'm not sure what reason there is for claiming that Pascha "could not come before the end of March". If Nisan 1 is reckoned as the nearest new moon to the vernal equinox (as it has been since Hillel II, and certainly this drew on what Jews already practiced in the diaspora), or according to barley ripening (which also occurred near to the equinox), a date of Nisan 14 would certainly be possible in March in non-intercalated years (i.e. in years without a leap month), with the vernal equinox falling around March 20. Only a reckoning that insists that Nisan 1 must begin after the vernal equinox would a date for Pascha in March be ruled out (since there is only 10 days to the end of the month, too few to accommodate the 14 days to the passover). However, I haven't encountered this kind of reckoning though it certainly could have existed before the standardized lunisolar calendar of Hillel II was generally adopted. BTW, Hillel II also had a slightly inaccurate dating of the equinoxes, adding in another relevant factor, as we don't know how the Jews in the diaspora reckoned the vernal equinox.
March 28 was the date of the JW Memorial in 2002. This is in accordance with Hillel's method of basing Nisan 1 on how close the new moon falls to the vernal equinox.
