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One thing to be mindful of is that oxidation through exposure to the atmosphere is not the only catalyst for molecular change in pigments suspended in an oil vehicle. That vegetable oils can turn rancid over time in a closed container is an indication that the substances are not inert.
I have not been able to relocate, but I will continue to search for, some long-ago read remarks about paints "cooking" or curing in the tube over extended periods of time. The product may look about the same and be physically usable, but some of the molecular change that should have gone into creating a strong paint film has already taken place. Metaphorically, it would be akin to putting small pieces of cured concrete into a wet mortar mix. The chemistry has long since taken place in those bits of concrete, which will serve only as filler in the new mix. And just as added water won't "reconstitute" the old concrete, neither will adding oil to cured paint produce a reliably long-lasting product.
I'd use the old paints for practice pieces or lay-ins, and begin putting in a supply of new, fresh paints for works in which you'll want to ensure physical integrity for a long time. In addition to the freshness of the paint, you'll have the advantage of many advances in formulations that have arrived on the scene only fairly recently.
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