And because the tube power curve isn’t linear if you reduce the power by 25% you don’t lose 25% of the tube power, but much less.
This is the curve I measured for my RECI tube (100W peak, 90W working), and at the recommended power setting (24mA, written on the tube) it’s at 75% of the peak output power but outputting a respectable 92W (almost exactly what the tube is rated for).
Notice how the power levels out at 100W – the advertised peak power. And the advertised working power of 90W is about exactly the recommended mA for this tube. When manufacturers use the peak power as the power of the tube they’re not ripping you off. You need that information to figure out the tube characteristics. The peak power is a constant from which all calculations are derived, and the working power is variable. So those advertising the peak power are technically more truthful than those advertising the working power because the peak power is an absolute whereas the working power will vary a few percent from tube to tube and over time. Those working with CO2 lasers know this and it’s not an issue for them.
Tubes are always outgassing and lose power whether you use them or not so it’s not worth fretting over it and just consider tubes an expendable item that needs to be replaced every few years when performance drops enough to annoy you.
Not to mention always cutting at the peak power and using just speed to adjust cutting depth not just makes it faster, but with less variables to consider, over time you’ll be more able to easily notice changes in the laser like if it gets out of alignment.