Transfer of registration for minor coming of age: custodial accounts

I thought it would automatically switch when the kids turned 18 or 21, but you need a medallion signature to get it all set up.

Banks usually have that service, but it required an appointment and it took an hour.

Seems clunky, but it was not too difficult.

What if I had not switched the name on account? Would it ever just change to the minor who came of age automatically?