Does anyone have stats on how many firearms are submitted and how many get approved by the review board?
I don't think there's a formal stat because so few are rejected. Until recently, an obvious exception was AR pistols, but no longer. The board is required to approve "well-made handguns". When I asked your question directly about 18 months ago, the answer was that just about everything submitted nowadays is approved. I was told which ones were "recently" rejected and why. The list was very short. Two, IIRC. Ignoring the AR pistol sideshow, the only ones that get rejected have a blatant issue like lack of a trigger guard or being obvious junk (usually imported, along the lines of vintage Rohm). For the most part, 98%+ of submissions are added to the list as little more than procedural formality.