PNA Shift Not Found error after loaded Retro record

I have reviewed the forum posts for Shift Not Found errors and it was very helpful.

I was able to confirm all of the configuration, however, our retro records came through with shift numbers for a subset of emplid's. Oddly these employees had current pay period shift earnings. For employees that did NOT have shift earnings in the current pay period, the retro pay earnings were populated with N for Not applicable.

Any ideas out there? Thank you in advance.