initiative happens at the start of entering combat not at the start of each round so your example isn't great because being put to sleep skipped a round but doesn't change initiative.
imo a better example would be a new goblin patrol entering the melee witch adds extra monsters to the combat [and they slot in depending on their initiative rolls]
p.s, that is also why a sleeping character doesn't get an action when they wake
for example you put him to sleep, then another goblin wakes him up before his turn in initiative order comes around = that ex-sleeping goblin still can't attack you... may do something else nasty of course
