Recently I found some old family photo albums that had been forgotten for years out in my garage. Though not exposed to water, the ambient humidity must have gotten somewhat high and many of the pressed together, facing pictures were stuck together. As I tried to pull them apart I noticed that the very oldest (1920's and '30's) of them came apart with gentle pressure and no damage to the the emulsion. I thought "Gee, they must have used some kick-ass hardener back then". Then I remembered that in my darkroom days, I would always mix my Kodak Rapidfix without the hardener because I was told that it permitted a more archival wash. Apparently those old guys had never been taught about archival printing because their emulsions are hard as rocks and after 75 years their casual snapshots still look like they were printed yesterday. What a bunch of dopes <g>.
Other observations, some of the later (1960's) B&W and color prints are going to have to be soaked to be separated. (I hope I can get some Photoflo somewhere). And, hands down, the absolute worst permanence offenders are commercial school photos. My advice is take any of them that you have and shoot copy negs if you plan to look at them when you are old and grey... or even youthfully middle-aged.