BMW R71 rear fender brackets (and fenders)

In an effort to learn more about the R71 rear fender brackets often seen on eBay, I posed the following question on the Vintage BMW list:

"There are two styles of rear fender mounting brackets on the R71, the one with the more delicate horizontal pieces that hold the hinged fender in position, and the heavier style that was copied by the Soviets on the M72. I've always wondered what determined which model R71 got which style of bracket. Was it an early-late production thing? Was it civilian vs. military?"

Here is a reply from Richard Sheckler:
"Most of the plunger series (R51, 61, 66 and 71) between 1938 and 1939 were civilian models to begin with and were built as such. Some (I don't know how many) of these bikes were delivered to various branches of the German government, including the army. Those bikes had civilian sheet metal.That said, there were at least three variants of civilian fenders for these bikes. A front fender with a shallow valence and shallow bell at the rear; a deep valenced and deep bell front fender; a shallow valenced rear fender, a medium valenced rear fender and a deep valenced rear fender. The two first types of rear fenders had hinged rear flaps with inside riveted braces with welded in place 8X1.00 studs that slipped into recesses on the lower tabs of the fender pillion rack supports and fastened with shouldered locking nuts. The pillion rack when fastened gave the fender its strength. The deep type fender had the rear brace riveted on the outside. This was done to reduce the tendency to rust through from trapped moisture at this point. These rear fenders were narrower than the Soviet M72 rear fenders. In late 1940 or early 1941, BMW resumed limited production of all four plunger models. It is likely that all were made for the government and intended service in military capacity. I have a rear fender here that I was told was made for a 1941 R71. It is similar in most respects to the earlier medium valenced fender except that it is as wide as a post war twin rear fender, and it has the rear horizontal brace riveted on the outside of the rear flap. In all cases, the horizontal brace is the same on fenders I have seen. I have not seen any that differed from these. I have seen heavier brackets on the Soviet bikes which I believe to be a Soviet design, not a copy of something made by BMW. There is another front fender that is in most respects the same as the post war R51/2 front fender."

An addition to being interesting and important historical information, it is useful for two things in particular, the first being a good spotting feature for recognizing a replica bike. (An "R71" on eBay with diagonal rear fender braces would be highly suspect.) The second thing is for re-enactors who wish to have more authentic looking machines.

Your thoughts on the subject are invited.