as far back as the 20202 -circa 1988 as i recall-blue and white-which i have
and my more recent wiemar set-
both of my sets have a total of 4
2 per car
not to challenge
it seems that 4 would have/ should have been the norm for a twin set,
as the gates' purpose is to block exit on the street side of the trolley rather than the curbside-
as each trolly has two entrances on each side-each unit should have had 2 gates for each car -ie 4 for a tandem set