I think your success with pad printing removal is being stymied because those Southwest Limited models use the direct-to-substrate inkjet printing method.
I'm not sure anyone has cracked that nut yet. But you're not crazy, it is different.
Yes, more and more companies are using this new method of decorating their models,. Micro-Teains as been one ot the pioneers, and nowadays they even ink-jet-print the intrigue sides of the cars (like billboard reefers). They also seem to have the highest resolution printer, which uses the thinnest ink.
I believe those inks are UV-cured, so they don't use solvents like standard Tampo inks.