It seems like a really widespread occurrence: quite a number of rent-regulated tenants who own income -producing properties out of state. They keep paying about 25% of market rate in prime Manhattan neighborhoods (Independence Plaza in Tribeca, UWS co-ops, etc.) Is it allowed? Is anyone interested, besides the affected landlords?

Why isn't it allowed? The tenant has to maintain the rent-regulated apt as primary residence, no restrictions on ownership of property or properties elsewhere. One's net worth does not enter into it.

And what is your source for any number you have who do do this?

"One's net worth does not enter into it."

But income DOES.

"It seems like a really widespread occurrence: quite a number of rent-regulated tenants who own income -producing properties out of state."

And, your source would be...??

My sources: I have to deal a lot with nationwide statistics, and I won't get any more specific.
About income/net worth, etc.: I said INCOME-producing real estate. Subsidized housing is probably the most widely abused program, and the abusers are not shy about it at all. Everyone knows it and nobody cares...