It's a little hard to count threads inside the sleeve, but I would guess the answer to that is "not quite".

Is that a good rule of thumb?

I was more concerned that the rotation of the chainring will be bearing on just the last 1.5mm of that slightly-too-short sleeve, where a longer set would spread over 3.5mm (although as I said, I'm not sure whether the whole assembly transmits loads that way or just via clamping force on the faces of the rings / spider).