Not ridden Betty Blue for years but I don’t remember it being under-graded (although a number of Glentress trails are in pretty bad condition at the moment- so it may just be that winter has taken it’s toll).
I’d say Glentress trails are slightly easier than trails of a similar grading elsewhere. With a lot of work at Glentress focusing on blue runs I wouldn’t be surprised if Betty Blue was renewed in the near future taking it back to more of a blue rating.
Again with deliverance it is a case of wear an tear I think- although they have been repairing some trails such as magic mushroom, pie run, and some other sections of the red back to their former states but it takes time and money (and trail fairy volunteers).