Zeboyd Games just said on Twitter that “According to SteamSpy, 1.6 million copies of our games are sold through Steam.”
Steam doesn’t permit developers to share their sales figures, to ‘protect other developers’ or somesuch. However, quoting the numbers provided by another website seems like it could be a good loophole for sourcing your sales figures according to a reliable enough website.
SteamSpy seems to be doing a world a good for developers by unchaining them from Steam’s bizarre rules.
Yeah, you could probably get away with that 
Main thing is SteamSpy obfuscates your sales a bit by including key redemptions. So although that figure has proven accurate to within +/- 10% or so (or even better), even if that figure was 100% precise you wouldn’t know the exact # of copies that were actual sales. For most games it’s pretty close as aside from Humble Bundle most people make basically all their PC sales on steam, but in our case I feel like we’ve done better than most at driving direct sales, which pumps a lot of key redemptions into our figure.
Not saying I wouldn’t use our steamspy stat with a wink and a nod if I had to…