"Is that unusual?"
Its not unusual that they wouldn't have the plans, although they have the plans for many of his courses. It would be unusual that they wouldn't have any historic documentation in a file on ACC (or Gulph Mills for that matter). There is plenty of histotical information connecting GM to Ross, including its listing in his booklet of projects (put out around 1930-31).
When researching within the Tufts, there are two major areas to search. The first place would be where they catalog his plans/drawings. The other area is the individual files on each Ross course, that contains old magazine and newspaper clippings, letters, old photos etc.
I would disagree with Wayne, the information is fairly comprehensive, especially if you are only trying to confirm Ross was involved in a particular project....which is the case here.