Alot. Because of the prior "troubles" at U, U pilots had a very bleak outlook for their futures on the eve of the merger, and had not hired pilots in years. The ALPA seniority merger policy takes this into account. 10 years seniority might sound like a lot at some airlines, but it might have meant you were furloughed or a reserve F/O at U, whereas it would have meant you were a Captain at HP. That is all considered when merging seniority lists under the ALPA policy.

Mind you, I am not saying the current ALPA merger policy is the best way to do things. But it was the "law" the parties agreed to and the arbitrator had to work with.