Before everyone gets too wound up, all this is in the JCBA and it should be no surprise it's going this way. But....

Pay is based on "classification date" not "occupational date". OD is seniority on the pilot's list and CD is for pay. Typically they're the same for LAA but they could adjust OD for LUS (or LAA ftm) to order the list without screwing with CD (as they should) and therefore pay steps.

One thing is for certain though, DOH would sure as hell be more simple moving forward and few will ever understand "why?".