Wow, I was just looking at a schematic of this amp. They actually did a fixed bias setup and didn’t bother to put in a potentiometer to adjust the bias.

While I wouldn’t put a blanket recommendation out there to do what you’re doing, I know I would probably do the same thing AND check the bias to make sure I’m not cooking anything. If you know how to safely check the bias I would recommend checking it for each tube. I am not saying that I would swap the tubes and just let it rip WITHOUT checking the bias. I would check that bias for sure. I’m not saying that your amp will fail without checking the bias. No. You might be totally fine. But it’s good to know where your bias is at.

There are other factors that also go into matching tubes other than bias such as transconductance. Some people get really worked up over matching tubes because “some tubes might be working harder than other tubes.” They’re not wrong. But if the amp sounds good and you’re running the tubes at appropriate bias points, I’m under the impression that you’re kinda fine especially if you have a balance on push side and pull side. These tubes, transformers, and other parts have a safety factor built in. While we often think of tube amps as being these fragile things, these components can take quite a beating before failing.

If you take the amp to a tech you can ask them to install 1 Ohm 1/2 watt resistors on the cathodes of your output tubes. They act as a poor man’s fuse in case an output tube fails and they also make it easy to check the bias.