OK. curiosity got the better of me. I took a random sample of 20,368 HS descriptors and just 131 were authenticated - that's about 0.6%.
The code I used is here: https://github.com/drgowen/tor-research-framework/blob/master/src/main/java/...
Best Gareth
PS - I only took a sample (rather than the whole batch) because each HS descriptor is in its own file and it takes ages to process - nevertheless, because of the way its collected the sample should be representative.