No, there is only one version and it's as simple as what I've said. "X" (as in chi) was used as an abbreviation for Christ from early times, perhaps initially as a camouflage for the religion. It was the first letter of the word Christos (meaning "the anointed one," e.g., the Messiah) and fortuitously was cross-shaped, so there seemed to be some symbolism or double meaning. It's been used as a scholarly and not-so-scholarly abbreviation since.
http://www.straightdope.com/mailbag/mxmas.html
I can clearly in my mind see the original claim I made. Sorry I can not place it in a certain part of my religious upbringing in the Episcopal, High Church experience...I feel it was a film and was dark and maybe a European village event. I wonder if it was way earlier in history. Christians have been under attack many times. I can picture the messy paint spilling slashes over the words.