MMBT vs. PMBT Prefixes for SMD Transistors

[Farley]

I notice there are (at least) two flavors of 3904 transistors with the SOT-23 footprint, MMBT3904 and PMBT3904.  Comparing the NXP datasheets of each shows that the specifications appear to be the identical. 

Is there a difference I am missing between MMBT and PMBT versions of this particular transistor? I've read speculation that the first letter (M or P) might refer to the original manufacturer. I've also noted that the single unit price at both Mouser and Digikey is slightly less for the MMBT version.

[T3sl4co1l]

P for Philips (NXP).

M for Motorola (On Semi), though everyone else makes MMBTs (and MMSD, and so on) too I think, so that one's more genericized I guess.

Other examples: MPS, MPSA, MPSH, MMBTH, etc.

There was a 2N3563 (something like a smaller, faster 3904), which was a TO-106 case (old 70s round plastic blob package), then the PN3563 (TO-92 -- as most PN's were: see also e.g., 2N2222 is TO-18 metal can, whereas the PN2222A is the TO-92 most people think of), and the Motorola MPS3563.  Possibly others I don't know.

Or the one popular in avalanche pulse generators: 2N2369 (TO-18), PN2369 (TO-92), PH2369 (Philips/NXP), MPS2369, etc.

Tim