According to the Microsoft PE and COFF Specification, section 4.5.6 (which I'm sure you have read closely if you're writing a linker), the sym= value is the COMDAT symbol, which is used by the linker in conjunction with the Selection value to determine which copy of the COMDAT section to keep in the final image. There are two entries in the symbol table for each COMDAT section. The first has the section name and an auxiliary record with the Selection info. The COMDAT symbol value comes from the second entry in the symbol table for the COMDAT section. It's either the symbol's ShortName value or the value of the string table entry it points to.
The COMDAT symbol value should be identical for all copies of the same COMDAT in the various object files to be linked. There should only be two symbol table entries with the matching SectionNumber for a particular COMDAT section in any one object file, if I understand the spec correctly. You shouldn't see multiple COMDAT symbol strings with different values as symbol table entries for a single COMDAT.