you'll feel most secure if you check it yourself.
With the lens off the camera, collapse it and adjust the lens to the two extremes of focus so you can see which position protrudes back furthest from the mount. Measure the distance between mounting surface and back of lens in that position.
Now prep a long narrow piece of paper whose width is the diameter of the back part of the lens. Measure the distance (that you noted in the step above) at one end of the paper, mark it, and fold the paper to 90-degrees on your mark. This will make an L-shaped tool. Lay the long dimension along your camera so it's flush with the lens mount and the 90-degree section points towards the shutter. Note how much clearance there is between paper and shutter, both front to back and width-wise with respect to the surrounding structures.
For me, end result was I felt comfortable collapsing my Summar 50/2 on my M8, though I still do it slowly.
Surely there are other more elegant ways to check, but this worked for me.