"Training for positive rate/climb identification is based on teaching pilots to recognise a positive V/S trend and increasing RA."
Two wrong statements in less than twenty words - pretty impressive even for a thread which is wanna-bee infested to a degree not often seen.
Neither of these things are "positive rate". A V/S trend is a measure of vertical acceleration. It will happily read a positive vertical rate with both main gear planted on the runway with say, a gross error in take-off performance calculations or wind shear. RA is valueless for rate as the reading which the pilots see is a product of an algorithm of pitch attitude and gear tilt and is by no means a direct reading of actual height.
The ONLY measure for positive rate is a sustained and progressive increase in the altitude displayed on the altimeter.
Should you doubt any of this, consult any FCTM from a company called Boeing. They've been doing this stuff for quite some time.