Matt,
I think it may boil down to an attempt to arbitrarily redefine how some already arbitrary terms are generally/historically accepted.
We've seen this throughout the history of the metal detector. ...
.(.Did you ever read about 'Flat-earth believers, trojdor?)
It appears that we have a few in this thread, reincarnated as metal detectorists !.....matt
The original term 'T/R' is used to designate an early transmit/receive unit that doesn't ground balance.
It's already inaccurate, in that the correct term is 'induction balance'...but we'll gloss over that, and simply state that because the majority of us accept that T/R means an older non-GB detector, we all understand it.
The later term 'VLF', generally used to distinguish a ground balancing unit, is by it's own wording totally arbitrary. 'Very Low Frequency'...totally nebulous term...has nothing to do with GB...but we all accept what it means.
(Note that the VLF still utilizes the same type of inductance balance to get a signal as the TR...only the processing is different...but that term was already used for the IB/TR, so we needed something else.)
Now you would like to take the term 'PI' and redefine it's generally accepted usage. You might even be correct in that your terminology is grammatically more accurate...but it doesn't matter.
Like the terms T/R and VLF, the generally accepted definition of PI has been in use for some time, and you can't undo history. It's already in use as a generally accepted term throughout the industry.
It's kind of like the joke; "They had to call it PMS because Mad Cow Disease was already taken."
Something akin to 'literal Luddite's' disease?..........Matt