I don't know how you know that your chameleon is getting enough vitamin A...and I doubt that anyone other than a vet who can give you an exact answer.
What I can tell you is that if the chameleon is given beta carotene (a precursor to vitamin A...aka prOformed vitamin A) its not possible to overdose it. The body converts it as needed. However its controversial as to whether any/all chameleons can convert it.
Then there is prEformed vitamin A...its ready to go and when ingested goes straight to work. Any excess will be stored and can build up in the chameleon and lead to organ damage, etc. Excess prEformed vitamin A may prevent the D3 from doing its job and push the chameleon towards MBD. You need to be very careful with the prEformed vitamin A.