in reply to Looking for appropriate Regex
If the sample data are exactly as you posted them (hard to tell since you didn't use code tags),
A B 1234 a,b -> ...
A B 1234 c,e -> ....
then it appears to me that you are dealing NOT with CSV. but rather, with SPACE-SEPARATED values (or, perhaps TSV if something in the writeup process transformed tabs to single spaces). If that's the case, you can't solve your problem by treating the data as if it were comma-separated.
OTOH (and again presuming that the OP reflects the data precisely), could this actually be CSV data with just two fields?
If you didn't program your executable by toggling in binary, it wasn't really programming!