Excellent news John!
If the solenoid plunger isn't able to move all the way in, it won't push the contact plate in the end of the solenoid into position to bridge the heavy contacts together to power the starter motor.
There are in fact two coils in the solenoid, one is a pull-in coil which earths through the actual motor (hence the motor turning slowly on the bench) and a hold- in coil which takes less current as it only needs to hold what has already moved - this coil is energised when the contact plate makes contact with the main contacts and bridges out the pull-in coil.
I suspect what may have happened is a ridge developed in the aperture where the solenoid plunger lives and it stuck momentarily (causing the click and nowt else) and the second attempt removed this ridge and the plunger went all the way.
As long as it keeps working then it's all good!