I have not even seen this thread before, probably because I was extremely busy at work when it was started in the first half of 2015.
As I have taken pictures of more than 600 Rolls-Royce cars over the years, I could contribute much more than I will ever have time for, but I will concentrate on examples with Austrian licence plates and post a few every now and then.
This is the oldest Rolls-Royce with an Austrian plate I have ever seen: a 1924 Rolls-Royce Twenty with a body by Cunard - picture taken at the Meggenhofen vintage car gathering in 1996:
Its former British registration was RA 5742.