James_Woods said: "only on passover day (a non-scriptural specification ..."
I agree with this statement.
Jesus simply said "keep doing this" Paul said "as often as" you do this.
And when discussing the Corinthian problems (1Cor 11:17-34) he said "when you come together... (for the Lord's Evening Meal)." There is no hint in any of that that this is a once a year memorial. If it was just once a year, you could easily describe the problems the Corinthians were having as poor prior planning for a once a year event. But Paul views them as ongoing moral faults.
On the one hand, the few directions given (for the Memorial) would allow for a once a year memorial view - or any number of times for that matter. But one has to wonder: Where in the NT is the direction for Gentiles to familiarize themselves with the Jewish calendar so that they can keep it on the proper day? - if thats when it HAS to be. "When you come together" and "as often as you [do this]" indicate a certain amount of autonomy on the part of the Corinthians.
In connection with the Christian view of the Passover, Paul said: "For, indeed, Christ our passover has been sacrificed. Consequently let us keep the festival (referencing the Passover), not with old leaven, neither with leaven of badness and wickedness, but with unfermented cakes of sincerity and truth." (1Cor 5:7, 8; Indicating, to me at least, that Paul saw the Jewish Passover as having a year round meaning for Christians. Coincidentally, the Society views the other Jewish festivals as having year round meaning.)
John (gospel, writing near the end of the 1st Century) mentions "Passover" 10 times. And 3 of those times refers to it as "the festival of the Jews." (2:23; 6:4; 11:55) That description of the Passover sounds like (again, to me) that there is some distance between Christians and this Jewish festival.
To me, this makes the whole Nisan 14/15 arguement moot.