On Sunday we caught part of the European Broadcasting Union's advent music jamboree, broadcast live on Radio 3. At one point we heard a couple of Christmas carols sung by an English cathedral choir. Afterwards the announcer gave full details of on carol, but the other was not explained. The carol in question was the arrangement of We wish you a merry Christmas from the Carols for Choirs book. This book has become so ubiquitous that perhaps the announcer did not think it necessary to explain. Certainly I recognised the arrangement immediately and could easily sing along, having performed it myself countless number of times.
With amateur choirs the use of the Carols for Choirs books is such that the arrangements of the popular carols from Books 1 and 2 are pretty well ingrained into folk memory. Proof of this came last night when we attended the annual Chelsea Green carols service. Whilst drinking mulled wine and eating food provided by the local shops, people sang carols accompanied by a choir from St. Luke's Church, Chelsea and a brass group. When it came to Hark the Herald Angels Sing and a couple of other carols, a group of young women launched quite unprompted into the Carols for Choirs descants for these carols. So natural do these feel that I am sure for many people, the carols without the Carols for Choirs descants feel rather odd.
So for a whole class of people, these versions of the carols are the dominant ones.