Hi,
Yes, you will be updating with old data - of course! But that may not be a bad thing, if the abends stopped all subsequent updates as well.
You might want to replicate these types of errors in Test (I assume the abends also happen there) and see what happens when you try to re-execute the ARFC updates after the fix.
It's amazing that this FM issue wasn't noticed in the Test system. Or was a transport missed when it moved to Production?
cheers
Paul