Without knowing how they measure, you have to (literally) play it by ear. If they sound good, then enjoy them. Obviously, you will need to re-tube at some point, so you might consider purchasing a new set of tubes now if it's in your budget. If you're really curious, put the new ones in for a few days/weeks to see if you notice an increase in performance. If you do, keep 'em in. If you don't, put the old ones back in and get more mileage out of them.
However, you say your amp sounds "glorious." In that case - I wouldn't change a thing!!
However, you say your amp sounds "glorious." In that case - I wouldn't change a thing!!