For the question When?
well, I noticed the first time the A appears is in "A" single (11.08.1999). The first A is different:
but... if you look well, the last side of the "A" is the actual symbol.
edited:
(like if you put the last side in a mirror -> hope I explain well hahah sorry. the pic is from the "A" booklet.)
anyway, in the single
"appears" (10.11.1999) the symbol A appeared in the actual format (idem like the LOVEppears album who was released in the same date).

PD: thanks to eneabba for this image.