Combined comments:
Bad, BAD Cenozoic stratigraphers! We let you get away with too much for too long! And now you want a period (or Sub-Era) whose
boundaries are NOT CONGRUENT with Stage boundaries!?!?
I thought "P" was for "Permian". Wouldn't it be the K/Pg boundary? (Or why not just the M/C boundary?)
Because C is the Carboniferous... :-°
Is the global Iridium layer unique? If so, I suggest "IL" as a substitute for "K/T" to avoid future modifications to stratigraphic nomenclature. Or, if not unique, but sufficiently unusual, then "IL1, 2, 3...". This assumes of course that no forward-looking scientists are going to change the names of the elements...