Some of the current-production 6550s have the original 35W rating (JJ, for example), which is why I asked for the clarification. Looks like all of the New Sensor 6550s sport the 42W rating (well, I can't say for sure about the Sovtek-labeled variant, but the others do).
As far as the new variants go,most companies seem to have done a cut and paste of some original-manufacturers spec sheet or just copied them verbatim. The JJ spec sheet seems to be most of the original T-S specs,anything New Sensor related seems to be GE. As to exactly what the actual specs are,who knows.
Just as an example,there was once (1980's) a beautiful looking Chinese made 6550.You would swear it was an exact (visually,at least) copy of an original Tung Sol.
Right up until you tried to use it.If it didn't fail almost immediately,and usually in a very spectacular manner,it produced virtually no output in any 6550 application. Maybe 40% to 60% of an original American tube.I never determined why,perhaps limited cathode capability,or perhaps the grid-plate relations were just wrong.In fact,there was a local shyster who was re-branding and selling these as Tung Sols!
Mind you,the specs I had said it was identical.
As we've all seen,many types on offer today are not even,in fact,the actual type they are described/labeled as,but whatever the manufacturer felt they could pass off as such.
And running them using the manufacturer supplied specs as maximum operating guidlines can be less than optimum,in terms of both lifespan and reliability.
Not very helpful,I know. I do believe someone once did a torture test and comparison of modern vs original 6550's,but I can't recall who.