So, to finally nail this Crossflow/CVH digression, I've had a look at my brochures for this period.
I don't have every single month, but I can narrow down the start of 1.1 CVH Escorts to after June 1981 and no later than October 1981.
The October 1981 brochure mentions the 1.1 CVH as a new feature for the 1982 model year, so probably started production nearer October than June.
June 1981 https://www.flickr.c...57632051739890/
As for the switch back to Crossflow in 1982, the May 1982 brochure very helpfully gives an exact date:
"1100 CVH not fitted to cars produced after 29 March 1982"
So the 1.1 CVH Escort is indeed a rare beast, being manufactured for at most 9 months.