A 'dwarf' cultivar will be labeled as such.

They were poorly labeled some were labeled dwarves some were not -all in the same area that said they were full sized. The folks at the nursery speak no english.

Bushhog,
You can go ahead and plant them and find out.
If they get too big for you, they take a good pruning of size very easily.
They have small leaves.
I bought a crape myrtle at HD on sale cheap, it was labeled
"Tonto".
It it real light baby pink, not a tonto, but I like it anyway.
Sometimes when you get something real cheap, you take your chances.
If you don't like them, you can always get rid of them later.