For a small company that's growing this quickly, it's probably going to take more than 12 months to know for sure if a hire is good or not. Declaring them as good does not make them so. I'd be interested to see a follow up post 12 months from now giving an update on retention rates and any hiring process updates they've subsequently made.
I have a pretty good sense, based on experience, whether someone is a good hire or not. You often know within 30 days.
My criticism was limited to your early declaration of victory on your hiring binge. The bottom line is that you can't know if someone is going to end up ROI positive until they actually get there. After 30 days you can tell if someone is a good dude and they can get stuff done, but you can't tell if some other company will come along in 2 months and poach him. Shit happens.
By building a strong culture you are taking good steps to minimize the chances of losing people, but you won't really know if you've succeeded with these hires until they are a net positive.