As I had suspected. I went out to my frigid cold garage, and looked at my "silver" anti-seize.
Mine is the silver aluminum type not the nickel type. I have used it for 40 years (still have original bottle) with no trouble but not necessarily on exhaust items. But, since I took the exhaust nuts off pretty regularly, no problem there either.
I think that the Nickel type, like the Copper type is specialized enough that neither are sold at the regular run-of-the-mill auto stores. I did find the copper at NAPA.
I am also guessing that the "silver" type that Chris Harris goes ballistic about is probably the aluminum type (like mine), not the nickel type.
In any case, Nickel seem to be the best for exhaust nuts, and Copper next in line with the aluminum last. Al three work, but Nickel has the highest temp resistance.
I also have suggested that when any of them are just sitting there in the can, they tend to dry out. A little oil (I use Marvel Mystery) added helps soften and mixes it up. According to all three MSDS sheets, all have the same liquid body - that of mineral oil.