Starting from the presumption that they're about the same across brands, one could add their own MSR float marks to non-MSR canisters.

Only reliable way I know to gauge the contents of partials is subtract an empty canister weight from the total when full. If I'm sufficiently bored I write the weight of new canisters on the side. And yeah, everybody ends up with a bunch of partials. I'll bet Texas hikers are happy to have those right now.

p.s. How did Korea corner the canister market?