Not sure I understand the difference fully, but the ILE Cobol Reference Manual for v5r2 says that COMP is used for representing Packed Decimal values and also that COMP-3 is for packed decimals too. The difference seems to be whether the length is odd or even, COMP-3 seems to be the one to use for odd field lengths.
If you’re not worried about viewing the contents of the field I think I would define the field as four characters instead of packed and convert it manually to numeric if and when I needed to use it.
All the best
If this is a mainframe COBOL definition, then I would expect that it should be understood under the COMPASBIN compile option — COMP-as-binary.
Mainframe COBOL generally handles COMP as a binary definition. Under OS/400 and i5/OS, COMP is packed-decimal. IIRC, COBOL compiles COMP as something like “the most efficient numeric handling for this platform”. Traditionally, that was binary on mainframes, but packed on the AS/400 line.
There is no distinction between even-/odd-digits packed.
This field is probably a 4-byte integer that may have as many as 8 digits.