Pm or not Pm, that is the question...

I look for the artist mark 1st. If it's not there, I assume the doll is not PM. From what I understand the original wax molds are destroyed while making the steel forms, and the steel wears away over time, so the mold becomes ineffective, and a new one has to be created. That's why some dolls, even with the same face mold look a bit different. It all depends on how 'fresh' the mold was when the doll was formed.
2nd, I've kinda figured out that the original molds had the lettering Pleasant Company in more of a casual style, rather than typewriting.
3rd, if the copywright sign is not in alignment with the lettering, it's an early mold. (PM)

Now, it gets tricky when the lettering is not casual, and the copywright is in alignment, I'll look for the artist mark behind the right ear.

When all else fails, and your'e not sure, look at the eyelashes. PC used modacrylic brown, soft eyelashes, Mattel uses a firmer black plastic eyelash.

If you're still not sure, press on the bottom of the foot, while holding the ankle. If you can squeeze the ankle at the same time, and it gives a little it is the softer vinyl, PM.

Let me know.