MD Anderson & Employment Verification

I'm not sure where else to ask this but figured this might be the best place since MD Anderson Cancer Center is in Houston. I was wondering if anyone here knows what the employment verification process is like for new hires at MD Anderson. How in-depth do they go?

So here's some context, please don't judge but it is what it is: I listed a former place I worked at that closed down years ago on my resume application to MDA (will stop doing this) and on top of that, it was work done for a friend's company and I was paid in cash. They were helping me get back to a working schedule after years of dealing with mental and physical health issues when noone else would hire me and I wasn't even earning close to enough money to have to file taxes at the time.

I guess I'm trying to prepare ahead for when the employment check is done and what I should expect or do for this particular job when it comes time for them to verify my employment. Any advice is very well appreciated, thank you.