Assuming this is 3rd, I'd guess the biggest hurdle for Crossbell is going to be whether there is a viable method of releasing them. I know XSEED can get by on low sales, but I'd have expected the sales of SC to be too low for a project of that scale. Maybe not? Or maybe it just defied all expectations and sold similarly or better on PSP.
Maybe DRM free sales on GOG are way bigger than we'd imagine for some reason? Those wouldn't get tracked on Steam Spy. Was SC on any other alternative PC marketplaces?
It's also possible that, while the sales themselves aren't great, XSEED has seen enough of a sales trend to justify green lighting The 3rd, knowing the pace of sales will eventually justify that? Maybe it's selling well enough to be worth doing as a goodwill gesture to fully cement the Kiseki western fanbase.
I imagine that Zero/Ao would be an easier project to sell than The 3rd since it's a completely new thing, so if SC did well enough to justify The 3rd they are a good bet. Not a perfect bet, for sure, but a good one.