score:3
Here’s a quick survey of selected chronicles and histories of England from the 14th to 19th centuries, with quotes illustrating how the writers refer to years.
You’ll see that the only writer I found who uses “A.D.” in running text is John Milton. This is a very small sample, but if it’s representative, then I think the most likely answer to your question is that there was never a period in which many writers in English used “A.D.”!
The survey suggests instead that the following trends or developments took place.
Writers fluent in Latin described years however they pleased, for example in the survey above we have Brompton’s “anno Gratiae” and Rudburn’s “Anno ab Incarnatione Domini”. But in other authors you might find “anno saluto Christianæ …” (in the …th year of Christian salvation) or “anno Christi nati supra …” (in the …th year after the birth of Christ) or other phrases with equivalent meaning. This variety declined along with the use of Latin, leaving only the conventional “Anno Domini”.
The year number was originally understood as an ordinal numeral. This is clearest in Higden where “Gratiae MCXXXVII” is parallel to “Stephani primo” (first of Stephen), not to “Stephani uno” (one of Stephen). However, when these Latin phrases were translated into English, the number became a cardinal numeral. For example Holinshed writes “in the year of our Lord 1555” and not “in the 1555th year of our Lord”. This change allowed the number to become a kind of name for the year.
Writers in English increasingly shortened or omitted calendrical prefixes over the 16th and 17th centuries, so that by the mid-17th century it was conventional to write years as plain numbers, leaving writers like Milton who used “A.D.” in a small minority.