Um, actually, no: the time period cut off of 1790 does not preclude the information provided.
At the request of a couple folks, I put together a packet covering the use of pyramid tents by civilians (mostly traders/merchants) and military from Queen Anne's War through the Ohio War. The packet included references to primary documents (including photographs of several of the documents), as well as photographs of drawings from journals dated 1754 and 1788, and a painting from 1781. The citations covered use at a couple of spots along Braddock's Road, and use in what are now the states of Maine, New Hampshire, Vermont, Maryland, New Jersey, Virginia, and Ohio.
As I wrote in my original post in this thread, it was a choice on the part of Fort Frederick. I suspect Tenngun has done a good job of outlining the reasoning behind the decision of the event organizers.