The fact that you say they stayed in the pots for some years is your biggest clue here. It's very likely they were extremely root bound when you put them in the ground unless you did some pretty extensive loosening of the roots. If that's the case, be patient. Feed them every spring and they will eventually break out into the soil and begin to bloom.
We planted some Natchez crape myrtles at our church eight years ago. A bulldozer just scooped out a hole, we filled it with compost and planted the trees in them. Without realizing it, we put them into a "clay pot". This was the 8th summer and this year they bloomed like mad and grew a foot after growing almost none all the years before and never blooming. Their roots finally penetrated the surrounding soil.
I heard Felder Rushing say on Friday that you can sometimes shock them into blooming by "beating them with a stick" (I'm not kidding), and driving a shovel into the ground around the root ball here and there to shock the roots a little bit. You've got nothing to lose.

As to an imposter: do the leaves look like the blooming one? Does the bark look like the blooming one? If so, they are probably crape myrtles. You may just have got some seed grown plants that are variable because of the different genetics of the seeds. This could also account for the fact that one isn't blooming. If they were started from wild seeds there's no telling what you will get. It always pays to buy named varieties.