For my last batch of albumen prints, I coated some Strathmore 500 2-ply and 1-ply, and while I find 1-ply much easier to work with and get much more even results over the whole sheet that way, I've been keeping the trimmings in an opaque bag, and I've noticed that the 2-ply seems much less susceptible to browning two weeks later than the 1-ply. If I had full sheets of sensitized 2-ply, they would be clean enough to print on. The thicker paper base and whatever adhesive is used to bond the layers together seems to be protecting the emulsion from oxidation. I'm sensitizing with a 15% solution of silver nitrate with 40g/l citric acid as a preservative. I don't know that this is enough of a factor to convince me to work regularly with 2-ply instead of 1-ply, since the system of sensitizing in the evening and printing the next day seems to work for me, but maybe if one wanted to spread the work out over a few days, that might be a reason to use 2-ply.