Illegal Usage Of Postage As Revenue Vs. "Provisonal Usage"?

Where does one draw the line between "provisional usage" and "illegal usage" (or "improper usage")?

Both involve the usage of postage stamps as revenues. My understanding is that "provisional usages" are during the very beginning of the implementation of a tax, before sufficient stocks of the appropriate revenue stamps are available. Is that an accurate definition?

What criteria determine a provisional usage vs. an improper/illegal usage?

Is it the presence of an overprinted, handstamped, or manuscript "I.R." as opposed to just a normal cancel (with respect to documentaries)?

Is it that in order to be considered provisional, it must have originated from specific businesses or in certain cities/regions?

Were provisional usages formally authorized, whereas simple illegal usages were not?

I've seen various overprints, handstamps, and manuscript notations described as provisional usages, but it doesn't seem like there are formal definitions or distinctions... at least as far as U.S. revenue tax use.

Some examples from the Philatelic Foundation of items they consider genuine "provisional" usages:

"Provisional" gets thrown around a lot. Technically it is an authorized usage of an available non regulation stamp for when the normally required stamp is not available. Sometimes it is because the stamps have not yet been printed and sometimes because someone ran out. Usually created with an overprint of some kind. However current year special tax stamps used to pay back taxes created by a manuscript change of dates are also called provisionals. The only genuine provisional shown above is the 8 cent Michigan Mutual. None of the others were actually authorized, they were just used. Of course it only mattered if the document they were on wound up in a legal action. Otherwise, no one who mattered legally would actually see it.

Well said revcollector, so it looks like the provisional's are: R153, 154, 155, 155A, 156, 157, 158, 158A, 158B, 159, and 160. I think what also gets in the mix is when the overprint changes the service designation like RG 28-36, RG %&A-E, RUJA 9-25 RJA 26- 29B, or the ST- stock transfer and FD - future delivery overprints.

There are many dozens of provisionals; taxpaids are full of them among other areas.