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You can. You change the profile shift or general tooth profile to avoid the undercut. And even if you have an undercut it's not the biggest deal. They're manufactured all the time. It's also noteworthy that min 17 teeth is only applicable to gears with a pressure angle of 20 degrees (as well as the no profile shift I mentioned).

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A downside of profile shift is that you get away from the pitch diameter. At the pitch diameter, there's no friction on the teeth, the further away you get, the more friction. But any hand drill will have a gear with less than ten teeth cut into the motor's shaft to drive the first gear, and they work just fine.

Positive profile shift on the smaller gear is actually usually how you optimize for minimum sliding/friction. The smaller the number of teeth, the higher your profile shift should be to avoid bad sliding at the start of the mesh.

Pitch point is where you have no sliding or friction which is where the operating pitch diameters are tangent, not where the individual gears have their reference diameter. (Operating pitch diameter can be slightly different from reference diameter depending on the sum of the profile shift coefficients)

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