If this claim was in writing then it's legally binding in most U.S. states. Technically it's legally binding even if it's not written but in those cases it's harder to prove.

Failing to live up to a business promise runs afoul of promissory estoppel: https://www.investopedia.com/terms/p/promissory_estoppel.asp

Right? When management demonstrates their inability to plan for repercussions, how am I to believe a pinky promise covering the next three years?

It was more than 3 years ago, but as far as I know, they did honor the agreement. Some people took early retirement packages closer to the end of that three-year period and they got the same deal.

> And people believed them?!

Probably because they could sue them for not keeping their word.

Why not? People believe the FDIC has enough money to prevent any bank runs from wiping and cash on hand. Very few check the tape, especially if they're in the middle of a fear or panic reaction and an authority claims its fine.