Answering question for Vacuum Tube - 5881WXT, Sovtek

Vacuum Tube - 5881WXT, Sovtek

The last time I bought two sets of matched quartets, one set showed lp 36 GM 4300, the other was lp 44 GM 4700. How do I know what soft/medium/high ratings are and what I should ask for when I place my next order? Also, do I need to leave them in the amplifier, turned on for an extended period to burn them in? Kind regards, Charles David