6550 Output Tubes Warmer Sound 12 months Later

I retubed my ARC Classic 120s in June 2018.  I have noticed over the past few months that the bass seems to have increased.  I listen to my system a lot....some days it is on 12+ hours straight.  I don't keep up with hours, but would suspect I'm around 2000 hours based on a crude estimation.  

I've been wondering what the signs of failure would be and haven't ever heard anything faulty.  I have heard of tubes warming up over time but never expected this to continue for a year up to the 1500-2000 hour mark.

These are my first tube amps and my first new set of tubes.  I guess I am just surprised and excited and love them even more now.

My post is to see how other's experiences have been and also to compare these Svetlana 6550 to the Tung-Sol reissues for the warming period.  I am thinking to try them next, but that may be a few years since these are just getting settled in.

Happy Listening,Dana
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You may be becoming accustomed to the wearing out tubes where the highs are becoming more rolled off lending to a sound that you actually prefer. This is where you need to put in a replacement set to get a feel for the changes you are experiencing.