No guarantees. The same thing that says that really old apartment buildings may have things that are nowhere near the current code. Depending on where you are there may be quite invasive inspections not only at the point when you intend to convert to rental use or periodically thereafter. For example in Highland Park NJ, I had to get the building reinspected on each change in tenancy (or some period). I can't tell you the number of changes I had to make that had existed for years, closers on doors, changes to the smoke/fire alarms, changes to the main panel... The building was origianlly a duplex that had one side renovated into two apartments.

Doing owner DIY work isn't a right in most places, it's just an allowed exception to the licensing rules.

And even it places where they allow the owner-occupant to make his own repairs, new work still requires permits and inspections regardless of who does it.

Permits and inspections - 5 A indicates that state law, at least, does not require a permit if, as I mused, the building has been re-declared a single-family dwelling. I don't know jack about the town I'm in now, but the place where I moved from has absolutely nil in the permit department (you need a BUILDING permit to erect a new structure, and I think the water people have some paperwork they require, but there's nothing electrical required), and the only "inspection" involved is the power company making sure your service isn't gonna blow the lineman off the pole when he hooks it up.

Conveniently enough, allowing the owner-occupant to do electrical work apparently isn't part of state law (either that or I don't have the spare brain cells to find it). However, We have always been allowed to do so.

Generally speaking unqualified persons are prohibited from doing work in multi-family dwellings. I guess the logic is that you can burn down your own house and kill your own family, just not another family.

As you described, there are any number of situations where an unqualified person may have been "legally" able to do work and then the property is converted into a multi-family dwelling. Of course the same kind of thing happens in a single-family dwelling when the owner does work and then sells the property. Substandard work can put life and property at risk. Not to mention there are probably thousands of owners of multi-family dwellings that do their own work illegally or hire an unqualified person to do the work.

The idea behind codes is to minimize risk, hopefully at some balance to cost, but no code (or law for that matter) is going to totally eliminate risk.

>>Generally speaking unqualified persons are prohibited from doing work in multi-family dwellingsMakes sense to me. But what makes one qualified? Years ago, I bought a rental duplex. Prior to the sale, the service had been upgraded by a licensed electrical contractor. Looking at one of the panels one day, I noticed several 14/2 cables, yet every 120V circuit was on a 20A breaker. All the wiring inspector could say was "Oops, I must've missed that. Sorry." The contractor claimed that his box of breakers must've been improperly labeled, even though every breaker clearly had "20A" on the toggle. At least they came right away and fixed their mistake. Who would have been held liable if there was a fire? If someone was killed?
I had another house that was almost entirely on one K&T circuit. Someone had tapped into the circuit in several places, soldering wires on for additional things, and covering the splices with MASKING TAPE!
The point being, anyone can make mistakes. I would imagine that most of the real boneheaded ones are made by incompetent DIY'ers, and IMO incompetence = negligence. But what about the DIY'ers who take time to read and understand the electrical code, plan a job, use high quality and proper supplies, route and secure wires properly, make tight connections, do box fill calculations, and most importantly - ask questions? We're still branded as unqualified in many circles. (But will still continue doing and documenting our own work!)