Its then possible to project how a movie in 1985 can do 95/05/today etc. considering those factors of inflation/no of theatres/no of shows etc. assuming that %% of fans and movie watchers remain the same.
Lots of projection studies for example in year 2030 are made in several avenues with data from 60's, 70's, 80's and so forth in many areas like global warming/oil consumption etc.
But for purposes of our issues here, its left as an exercise for the reader :)