Regarding the two ticks prior to the shutter tripping on my Nikkormat, once they tick they stay that way until the shutter is tripped, even if pressure is taken off the release. For example, I can press on the release button to make the first tick, take the pressure off, then again for the second tick. At that point the release has much travel but the next effect will be the shutter tripping. Another example, if I am waiting for just the right moment, say for a bird to fly into the frame, I can press partway down to get my ticks out of the way so that I can trip the shutter smoothly and promptly.
So I am still wondering if this is a common feature of the Nikkormat, or peculiar to my particular camera.