Some progress!
In the same bag of transistors, there were two Motorola transistors marked Motorola (logo) K68MEX, datecoded '85.
Presumably, these are equivalent to the RCA K68 since they (a) were found in the same bag, and (b) have similar part numbers (K68)
Sadly, searching for the Motorola part number yielded no results either... but at least it is clear that the part was made by more than one manufacturer. Is it perhaps less likely that it was a custom marked part if it was available from two different manufacturers?
I would guess "MEX" meant the devices were manufactured in Mexico, as I have seen that suffix on other more well known types.
We often received mixed bags of devices, some with "MEX" on them, & some without.
Very early RCA devices used the prefix "CK", maybe an early Silicon power device, with the "C" omitted?
I know most early power devices were germanium PNP, but there were definitely some odd types out there.
Some very early "transistor radios" had NPN germanium small signal devices, but they were pretty much swamped by the flood of early PNP germaniums in the "OC xx"series & their "2Nxxx" & "2Sxxxx" counterparts.
Philips & Mullard actually made a few
real "bipolar transistors" (they had interchangeable emitter & collectors for "special applications", the details of which are lost in the mists of time.)