I guess that there is no regulation that requires a buyer to record their assignment, but what is the risk to a holder of a NPL when they do not record their assignment? 

One BIG problem with condos is their regulations.

Real Estate Regulations article 1 section 10131.Broker Defined (What does this mean if there are any lawyers out there)(e) Sells or offers to sell, buys or offers to buy, or exchanges or offers to exchange a real property sales contract, or a promissory note secured directly or collaterally by a lien on real property or on a business opportunity, and performs services for the holders thereof.what does this mean for wholesaling.

Tricks of the trade or "best business policies".Landlords must without exception be experts on their state landlord tenant regulations.

Or they know that thanks to regulators foreclosure now take forever, and that they are going to get to stay in their homes for 1-2 years without making a payment.

There's plenty of post office regulations to google but what works for me is:Line 1 - This can be anything, person or corporate entity, or even blankLine 2 - Must be just above the city and either PO Box or physical street addressLine 3 - City, State, Zip CodeThere are also websites that scrub and correct mailing addresses. 

(We haven't even touched on zoning issues and the growing number of city regulations around STRs.)

There is a Fair Housing regulation that says if you hire a 3rd party to conduct fair housing testing on you, the fact of the testing, and the results, are absolutely privileged.

Fair Housing Regulations is a Federal Law under HUD which is applicable to every State.There may be State specific conditions also, but they can not countermand the Federal's.The gory details of FHR is found at the ECFR Gov Publishing Office site. 

I want to do a shared well (private water supply), and everywhere I look on the Mass DEP regulations, there are no prohibitions regarding shared wells.