AD/BC became so widely used that it lost its religious connotation and became a generic indicator of an accepted time reference frame
Agree. How often do you see "C.C." at the bottom of a letter preceding the name of a person who is copied on the letter? Does anyone remember that "C.C." is the abbreviation for "carbon copy"? Does it really matter?

I worked for Xerox for a time and they used to write "X.C." at the bottom of their letters, but it never caught on with their customers.