Very interesting.
If you guy's ever get to the point of merging those lists, you get to the problem of how. At KLM and fully owned daughter KLM Cityhopper this has been done. They picked a date, say today, everybody already working at Cityhopper gets half seniority at KLM (to be used after 8 years) and all new hires will get full seniority on the new list. With a sliding scale for those working less that 4 at Cityhopper. So the guy that has been with KLM for say 2 years now has a lot of Cityhopper pilots in front of him on the list. He is not a happy camper. It won't influence his short term bidding but down the line it might take him years longer to make big-jet-captain, and associated pay. So what do you think happened ? The senior Cityhopper guy's started a lawsuit saying they deserve full seniority as well (date of hire), and that the junior Cityhopper guy's got a better deal and that is discrimination. Go figure. Case is not settled yet. If this tread is still alive I'll let ya know.
(P.S. I'm not personally effected).