I wouldn't worry to much, first time parents have a very high risk of pulling the first joeys, a lot of times the human may not have any idea they even produced.
This can happen for many reasons, poor diet, living conditions, not ready to be parents, something not right with the joey, stress etc.
If she dropped or drops joey in pouch..
Mom licks a trail from her cloaca to her pouch. The joey travels up the wet trail to her pouch climbs in and latches on to a nipple.
The pouch will feel like there is a round hard spot in the pouch the size of a head of sewing pin.
As it grows it looks like a lima bean size lump and continues to grow until its parts( tails or legs ) start sticking out of the pouch. Usually Unless you witness the birth, you won't notice until it's the size of a lima bean or peanuts in the shell if there is two.
But again, I wouldn't worry to much, he could have been a late bloomer and they may not have bred. There is just a risk that they have and that they will produce.