I've heard referenced in a few places that some of the books have issues with the use of the terms upgrade/increase and downgrade/decrease in that they're using them interchangeably. Does anyone know of any specific examples of these mistakes?

I haven't heard of that, and I've been here since late in the EotE beta. It seems unlikely...more likely that someone complaining doesn't really understand the difference.

In any case, I think it's fairly easy to adjudicate: use an upgrade/downgrade if you want to keep the basic chances of success roughly the same, but increase/decrease the chances of advantage/threat/triumph/despair; use an increase/decrease if you want to change the basic chances of success. Changing the size of the dice pool has a much greater impact on chances of success than upgrades/downgrades.

Yeah, that was my thought, as well, which is why I was curious to see some actual examples. Thanks!