...Other than the potential damage that could occur from incorrect mounting, I still have not heard a compelling arguement why these photos should/could not have been mounted.
If we are framing for the photographer and the worst happens, then getting a replacement image may be no big deal, and that seems to be the case in question here.
Dry mounting, even though it may become familiar and routine, is still a complex process, and once in a while we make a mistake. More seldom, something unexplained could happen.
Other than the risk of damage, I don't know of a "compelling argument" against dry mounting.
The problem I described would be more likely if the images were no longer available and re-mounted later. In that case, caution would be advised, especially if the images had been damaged from improper previous mounting. The potential for damage or destruction is a powerful disincentive for those of us who have suffered with our mistakes in the past.
Instead of using corner pockets at all, with or without hinges, I would prefer to use edge supports made of paper or clear film. That mounting method is fast, cheap, secures all edges, and allows expansion/contraction.
After several years of edge-mounting collectible photos, I have yet to see a problem come back later. However, non-invasive mounting requires
careful fitting. The insulation provided by back-filler and a tight dustcover slows environmental changes.
Slightly-loose fitting points avoid restricting movement of the paper's edges under the mat. Too-tight fitting points are a popular mistake, and
that may be the most common cause of cockling or ripples on photos and other papers not dry mounted.
Dry mounting, done right, eliminates the detrimental effects of too-tight fitting or an unsealed frame-back.
As usual we have choices, and there are ups and downs with each choice. Rob, you prefer the certainty of dry mounting, and "compelling arguments" against that mounting strategy are lacking.
Personally, for items of value I prefer minimally-invasive mounting, with careful fitting to avoid the problems some framers consider unavoidable.