sequential numbering
 

I am trying to create a membership number based upon a date of
payment. Potential clients names are collected and entered into column
B. The date of their first presentation is column C. The date of their
membership payment (most important as they are NOT allocated a number
until complete) is colum D. The membership number is allocated in
column A and is based upon a date entered into D. I have so far:

IF(D3="","",COUNT($A$1:A2)+1)). This creates a sequential number BUT
changes when a member listed above in order makes a payment. Is there
a way to allocate a static number to a column with reference to
another cell?
thank you - majestyk