Programming replacement keyless entry transmitter

I successfully programmed a new original factory replacement transmitter, for my 1997 Chevy Cavalier, which is working fine, however in the process my 2 existing transmitters are no longer functional and unable to be programmed despite following all instructions on numerous repeated attempts. Any thoughts?

Read the instruction very carefully. You might be doing something wrong.

That is strange.

Normally when you have at least one remote properly programmed and working correctly you should be able to program a few of them.

I don’t think removing the batteries and replacing them in those two remotes will do much, but it won’t cost anything to try.
Reprogram the remotes again after reinstalling the batteries. Are the batteries in good condition?

I don’t know about the Cav, but with some vehicles all remotes need to be programmed even if you are adding one.