If you want it to go beyond d, it's very simple. Just change these two lines:
... now it will properly do lower and upper case from a to z.
As for the last variation, give that some thought or get in touch with whoever is doing that and get them to standardise.
I know that you say that you can't enforce standardisation at the moment, but you can try and reach out to those involved, especially those with not so ideal formatting. At least some of them will listen.
Code:
Const RESP_1 As String = "[a-[COLOR="blue"]zA-Z[/COLOR]][.)]"
Const RESP_2 As String = "[*][a-[COLOR="Blue"]zA-Z[/COLOR]][.)]"
As for the last variation, give that some thought or get in touch with whoever is doing that and get them to standardise.
I know that you say that you can't enforce standardisation at the moment, but you can try and reach out to those involved, especially those with not so ideal formatting. At least some of them will listen.