At DL, they are pay codes for violations of the contract, making you “whole” for their mistake. Originally, they pointed to the section of the contract violated. Over time, some of the sections have ‘migrated’, but the 4-digit code remains as originally put into the Commodore 64.

The ACE app used to have a decoder ring. 4F1C is generic ‘removed for company convenience’, and 23G5 is ‘OE buy off’ for FO’s.