Go test them before you turn on the amp.
make sure it close in reading , if don’t have tester just buy new one .
black or dark round is mean used lot , shiny is new look.
better buy match tubes .
Shops that sell and repair musician's amplifiers will have tube testers.The dark spots happen when the tubes are used.It doesn't mean they are bad necessarily. Gold Lions are not rare,they can be bought new from any retailer that carries the Genelex brand. I'd be curious why an amp that takes four power tubes was sold with only two tubes included. If two went bad was there a problem with the amp?It may need to be serviced
Are the circles silver/black? If so it’s perfectly normal. Some tubes have them on the top, some have ‘em on the sides. It’s all part of Getter , shoot, I can’t remember the exact name. As the tube ages, it will get smaller. That’s one way to know when it’s time to check your tubes and see if you’re getting near needing to replace them.
All the best.