well
I was hired in 1988...my airline then bought two other airlines and went date of hire even though one of the airlines was out of money.
then another airline and mine got together and people hired AFTER I got hired got placed senior to me...so WORSE THAN date of hire.
After another merger, people with 7 years seniority were placed ahead of me when I had 23 years seniority. MUCH worse than date of hire for me.
so, I've seen it all...except of course benefiting me.
I didn't mind date of hire in the first two mergers/acquisitions...but when date of hire suddenly wasn't good enough for the last two...I had to say: WTF?