If you want to publish a research paper, "Yeah, I know this isn't really a valid measurement, but it's the best I can do" isn't going to cut it. This isn't a research paper, but honesty is honesty. If those are the best numbers you have, I would simply not say "X% of enteprises are using" -- because you don't actually know that. I'd say what you know instead, however you can describe it. Yep, it doesn't read as well marketting-wise, true.