Add cristate to the mix. Cristate is used to describe one kind of deviation from 'normal' which results in something of a crest. The deviation may be such that it is described as monstrose. Such a broad term may even include leaf color variations or variegation. I wouldn't think there would be lots of agreement, but a cristate plant might look monstrose (monstrous), display a crest, or have leaves not completely green. Yale

As I understand it, the monstrose generally refers to the leaves being contorted or not resembling the parent plant.
In the case of cacti, they will look as though they were made of clay and someone pinched them into a new shape...so hard to explain.

Crest forms are, generally speaking, a wide stem base which will in turn carry more plant growth along the top (if it has leaves).

Some plants are both...

This is an example of a crested Dandelion that I found in my yard a couple years ago...

{{gwi:511903}}

See, that's the thing I keep running across. Monstrose is mentioned for something monstrous yet I've seen Monstrose used for a plant that has come from another plant yet retains its own look.

I am a bit confused by that...Do you mean 'monstrose' has been on the label, when you didn't see a difference from the original version of the plant? It is very common for labels to be wrong....

No, I'm just trying to figure out the terms that are used for certain plants.