Nope, in the current implementation PWM runs at fixed frequency (10 kHz), it is the duty cycle what is changed - so you'd have to measure pulse length between opposite edges (rising - falling).
Thanks, CW2, I've now achieved that with Port.InterruptMode.InterruptEdgeBoth (and modified my post accordingly) and the test output now stacks up (which I have also edited to show the proper output) ... but having said that, I'm still to properly get my head around the implications of duty cycle! But it is nevertheless very good to see that PWM OUT is approximately equal to the same signal taken back in as input and then measured via interrupts!
Additional Edit: Thanks to your prompting, I've found an excellent PWM tutorial, and an excellent Servo tutorial by the same author, and once again modified my post accordingly, as well as adding those two links to it. Thanks again!