Marc,
That old myth that tumbling cartridges will change the internal powder/burn rate has pretty much been proven incorrect. At least that is my understanding .Some folks took some freshly loaded ammo and tumbled it for 48 hours and then ran it over a chrono against identical, non-tumbled ammo, and the velocity was identical. No pressure spikes.
If those old cartridges were mine, I would put them into my tumbler with corncob and brass polish and give them a good cleaning. Some handloader use a liquid car wax, like NuFinish(cheap to buy) in their corncob media, and they feel that it not only cleans the brass, but it deposits a coating on the brass that help keep it from tarnishing so quick.
I have tumbled loaded ammo for many many years with no deleterious effects to me or my ammo. YMMV
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