Your PRIA will take 30 days because they won't respond, and you need to have proof of employment (tax returns or similar) because they likely won't answer those requests either. Apart from that, you won't have any issues.

You should have no issues... We have had guys go back to UAL, 5Y and several other USA carriers... Like others have posted just took HR a few extra days for the clock to tick by with no reply... Good luck and enjoy your return to the big PX...

Cheers

No issues:
I worked in the Middle East for a Flag Carrier.
Make sure your keep every piece of paper the give you along the way, like training records, check ride forms, and atta-boy letters if you saved the day.
(I did: Flew on a day off on short notice, got a nice letter in the files)
It is a different world over there in the sandbox. The Magic Kingdom..

i have had a different experience with this. In 2012, I interviewed at a large acmi carrier in Miami with offices in purchase, ny. I was working overseas and the interviewing pilot was very aggressive about getting my PRIA from my current employer and condescending about their ability to produce one. I would go so far as to say they were hostile and overtly racist. In 2017 I was at a job fair and speaking to fed ex. They would not accept my app as I had been overseas and needed to have resided in the US for the previous 5 years. This is no longer the case, but it is my experience. I think times have changed, but it wasn’t all roses for me.

Yes, it's changed for the better. Also the five year residency thing was not FDX (or any other airline) policy, it was a USPS requirement. It applied to everyone except mil or USG employees assigned overseas on official duty. That policy has also been rescinded.

I've heard that the post-CJO background check company requires past W2s. Having worked in the Middle East for the past decade and a half, I obviously don't have any. Will past tax returns suffice, or what else could be submitted in lieu of W2s?

Anything that confirms you were employed somewhere during that time. Tax returns work.

I wasn’t required to submit W2’s or tax returns. They contacted my overseas employer by email and verified the dates.

Same experience.

This works only if the overseas employer responds. Many foreign carriers do not.