Nero UDF & UDF/ISO confusion

I have tried various techniques of making an incremental backup CD-R
with Nero 5.5.10.54 using UDF and UDF/ISO formats. I mainly want to
backup digital camera photos as months go by, filling up one CD-R at a
time.

I have "Multisession" checked and everything seems to copy fine
(different files on different days, with the original Nero compilation
saved each time to retain the layout), but many of the files end up
corrupted on the CD-R even though the sizes and names are accurate.
They become unreadable, even with an app like ISOBuster. When I open a
UDF CD-R in ISOBuster I see many different sessions, some with corrupt
files, some without. Usually the corrupted files begin after a certain
date, whereas previous sessions seemed to save with no errors. I
really don't understand the format.

Is Nero UDF or UDF/ISO actually _designed_ to be used for incremental
backup like Nero InCD or Roxio Direct-CD? Years ago, Direct-CD never
gave me problems but I've gone the Nero route for various reasons.

Several CD-RWs formatted with Nero InCD have crashed on me (could be
InCD, could be the brand), which is why I've been trying to use UDF or
UDF/ISO as a substitute. Is there a good FAQ for this somewhere
instead of the scattered forum questions I've found? Nero's program
help is very limited.

K2