Append Query – Already Done

I have a table (call it Table 1) with names & dates & payments in Access 97 (There is an entry for each month). From another Table Call it Table 2), I have the same names, and the current amount.
I made an append query which works well taking the current data from Table 2 and posting it to Table 1.
But I want to make sure that this posting process is only done ONCE for the month. (I always enter the first day of each month as the date).

Is there some way to test for the presence of the month’s data and then stopping the append before it is done twice???

Any help would be greatly appreciated!!!

abramowitza@coned.com