Support Shaft Splines Don't Match TC

I'm installing a new torque converter(TC) into my TH350 and though the 30 spline input shaft matches up, I'm noticing that the 'support shaft' splines (not sure what the technical term here is but its essentially the pump splines) on the TH350 has 27 splines where as the new TC has 21 small splines with 3 large splines (spaced 120 degrees apart). I'm not sure if this is a mismatch or not, please advise. Thanks!

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that is getting to be more common in modern era stuff-allows oil / lube flow better------

Hmm, interesting. Thanks!