Earlier quoted context omitted.
Unless current employer a) receives your permission to pull your tax return transcripts or b) receives your permission to contact your previous employer and you provide permission for previous employer to divulge said information, you will almost surely not be found out. Disclaimer: Not a lawyer, not your lawyer, but fairly confident based on past experience with this over ~15 years.
you will almost surely not be found out. ... unless, like patio11, you decide to blog about your salary history at some point. The problem with lies is that you need to remember what they were so that you don't contradict yourself later.
patio11 is unusually (yet refreshingly) open with his financial information.
If you're going to blog about your intimate financial details, you should of course "have your ducks in a row".