No, there really is no reliable way of telling in advance. If the tubes are used a very long time they can sometimes simply get weaker. Dynamics and extension suffer. But these changes can be so small and gradual over such a long period of time you may not even notice.
If you are concerned at all then the smart thing to do is just order another set of tubes. Put the new ones in and if it turns out sure enough the old ones were shot you will know it right away. Save the old set for backup. Or if they sound about the same do whatever you want. If it was me I'd run the old ones as long as they last, maybe comparing them against the new ones every once in a while, until either one goes or they start to sound weak. Either way you keep your backups so you're never SOL waiting for tubes to come.
If you are concerned at all then the smart thing to do is just order another set of tubes. Put the new ones in and if it turns out sure enough the old ones were shot you will know it right away. Save the old set for backup. Or if they sound about the same do whatever you want. If it was me I'd run the old ones as long as they last, maybe comparing them against the new ones every once in a while, until either one goes or they start to sound weak. Either way you keep your backups so you're never SOL waiting for tubes to come.