Excel 2007 : Using nested logic in a formula that partially monitors previous results

I've been struggling for most of the morning trying to create the logic for the following problem.

Here are the conditions I'm trying to monitor with a formula in the cells of column 2.

1) If the date in column 3 is greater than the date in column 4, then all is OK.

2) If the date in column 3 is less than the date in column 4, then that is No...unless the number in column 1 was the same as the one immediately above it and that one was OK.

So, to clarify...in row 3 of my example, the column 3 date is less than than the column 4 date and the number in column 1 is the same as the number above it, but that result was No. Thus the result in row 3 column 3 should be No.

In the last two rows of my example...the column 3 date is less than than the column 4 date and the number in the first column is the same as the number above it, but that result was OK. Thus the result should be OK.


204133 OK 8/5/2010 7/26/2010
204137 No 8/5/2010 8/6/2010
204137 No 8/5/2010 8/6/2010
204151 OK 8/5/2010 8/4/2010
204273 OK 8/6/2010 5/30/2010
204273 OK 8/6/2010 5/30/2010
204277 OK 8/6/2010 5/30/2010
204277 OK 8/6/2010 6/1/2010
204310 No 8/6/2010 8/9/2010
204559 No 8/10/2010 8/11/2010
204570 OK 8/10/2010 8/6/2010
204614 No 8/10/2010 8/11/2010
204637 OK 8/10/2010 8/8/2010
204637 OK 8/10/2010 8/16/2010

Assuming the data starts in row 2.. if not insert row above... then in B2 enter:

=IF(OR(C2>D2,AND(A2=A1,B1="OK")),"OK","NO")

copied down.

Mine also was posting not seeing shg's request... I have now unhidden it for another alternative...