I'm thinking that perhaps the loan was sold and resold and resold again and somewhere along the line the paperwork got lost, or was declared invalid in court, so the bank couldn't prove they had the right to foreclose.

His agreement to "let you walk" provides nothing of value to him, to it is difficult to convince a court of law to agree that his agreement to lose out on money is legally binding.

I would get a letter inviting me to small claims court or something?

While not explicitly stated in the tax code that I am aware of, this has gone to court several times in the favor of the taxpayer.

And is it worth the $50-100 to take them to small claims court? 

If I go to the court house, will the bank be listed on the deed ?

I went to the free DC Court search and typed in the tenant's name and the 3 eviction cases and documents filed popped instantly to my horror. 

The LP is easy to find, on the Dade clerk of court, official search, site.  

It took me nearly 5 months to get paid and that was after a letter saying I’d take him to court.

And the general consensus seems to be that renting in MA can pose bigger issues with evictions and the courts.