I don't know that much about the license thing other than a handful of spas in the GTA have some kind of limited holistic license (I believe these are mostly the premier "holistic" places). But you're right, it's mostly the type of services offered that dictates whether it's semi or holistic. Semi places generally want to provide a decent massage with a bit of fun at the end but there is a lot of grey area within semis and some places are known to be a bit more "liberal" than others. In fact, the same MPA might only offer a basic HJ and some light touching at one semi spa but will do more at another (often, this is due to how strict the boss is). But at a minimum, you can expect at least a basic HE at a semi place (otherwise, it would be a legit clinic such as CBQ or any number of RMT clinics out there).
Like you said, because there is more focus on the "massage" part, many ladies > 40 can still do quite well at semis, and customers also benefit from not having to pay as much tips for basic extras too. Having said that, there are many younger ladies at semis because they don't want to do the higher mileage stuff at holistic places. I was just talking to a regular MPA of mine the other day and she was telling me that one of her friends keeps trying to convince her to go work at her holistic place because she would make much more money but she doesn't want to (because she doesn't want to "have to do" those higher level services for everyone).
Most holistic places will also give you some basic massage at the beginning as well but the quality won't be as good compared to the semi places and many guys will not even bother with the massage part at holistics. Also, keep in mind, everything I've been talking about is generalities here. You can certainly get BS, BJ and FS at semi legits but the difference is those aren't are a part of their standard services and the MPAs will often only do those with customers that they like (hence, the YMMV concept) and/or those that provide big tips. Contrast this with holistic places where anyone can walk in and get FS, since that is part of their standard services.
Also, many guys on here talk about getting extras at legit places. This is not as difficult as it seems. As XTC alluded to, there are many semi legit MPAs that also work at legit clinics. If you get to know one of these ladies really well at a semi place, chances are good that she will provide you a bit of fun at the other place too. It is more uncommon if we're talking actual RMTs, but that happens too.