Hi there.
Firstly it is unlikely that any damage has been done unless the guy forced the knob past the stop - the reason KMZ state not to change the speeds with the shutter unwound is most critical to the Zorki 4K, which has the additional slow speeds escapement, and damage almost certainly will be done if speeds are changed before winding the Zorki 4/4K shutter.

Best way to check the shutter initially is:
1) WIND THE SHUTTER - then set to 'B' with the back removed. Fire the shutter, hold down the release button. The opening curtain should snap smartly open. Now release the button and the closing curtain should close quickly but not quite so snappily as the opening one. The secret of the Barnack shutter is that the closing curtain moves slightly more slowly so as to avoid it catching up with the opening one and causing fade. If the shutter is snappy at the 'B' setting then other speeds should be reasonable. If sluggish then a lube/adjust is needed.
2) Now set to the 1/500 speed, back off and lens off, and look through the lens throat. Aim the camera at a grey sky or well lit light coloured wall and fire a few times. You should see an evenly lit oblong. If you do then things are looking good.
3) For an approximate way of testing shutter speed accuracy, check Rick Oleson's page http://rick_oleson.tripod.com/index-135.html +/- 20% of the set speed is allowable, that is only 1/5th stop.

Hope this helps,

Steve