I would say as long as the cylinders were sealed and still held pressure they would be fine. If they've been sitting open and empty I'd say they'd probably have unwanted moisture or rust inside and I would just replace them. But if they are still pressurized I'd use the gas then have the cylinders hydro tested to be refilled.
As far as co2 cartridges I would think they would be primarily for dispensing. I would think it would take too many of them to carb a full keg. But not having tried I really couldn't say either way.
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