Update question

It's been a while since I've done an update program and I know I should know
the answer to this but I don't.

I have a program that reads an update file sequentially and writes to a
master file. After it reads a record from the update file, it chains out to
the master file. If no record was found with the same key it writes the
record to the master file with a WRITE. If a record was found with the same
key, it check 4 other fields to see if this is an exact duplicate. If it is
an exact duplicate it discards the record from the update file. If there
are difference in the 4 fields, it writes the update information by moving
the data to the master file's record and does an UPDAT. I should also
mention I've put code into the program to print the update record and the
master record when it finds one it is going to update.

I ran the program and it shows 200 records updated. I ran it again and it
again shows 200 records updated. It is apparently finding the discrepancies
but not really doing the update.

My question is this: once I find the differences, do I have to CHAIN again
to get the proper record in position to update?

TIA.