Coach Question for Miko Trento

Got an email from Earl who was reviewing the 16mm footage, and has this question for you after looking at the 1965 footage.
Qustion for Trent would be how come in 1965 there are no open gons on the Silverton? They had 3 of them built in 1963. Every train I know of after then had at least one of them.
Earl also confirmed that the stuff we thought was 1967 was 1968(Durango turning loop, etc) and that the last shot was probably 1971. We aren;t sure where the years split though on the film.
I also sent him some footage from another source showing 473 switching freight in Durango, and he said the shot was the bridge on the old Rio Grande Southern lead, so that was interesting.
Still waiting on some more info from Earl when he gets home, so project is once again on hold. Thanks for the help Mike, and Earl!
Greg Scholl