O.K. it seems when I got my new Martin OM (not my Collings) that when I would play on the high E string around the 3rd thru 5th frets it would sometimes slip off the fretboard. I took it to alcal shop and he diagnosed it as too close to the edge. So a new nut was fashioned. It was spaced way too narrow for the 1 3/4 neck. So i took it back and he did another one. Much better but it still is off by almost a 16th narrower. is this being too picky or should I be expecting to get the same spacing as close to specs as possible?

Nope, you're definitely not being too picky. The nut is the heart of a well set-up guitar, and your repairperson should not have got the spacing wrong. 1/32", let alone 1/16", can make a noticeable difference.

In your shoes I would politely request one more attempt to get it exactly right, for free if you’ve already paid, and if this one fails I would invest in a trip to a better repair shop.

There is also a possibility that the nut was re-cut narrow because of a slight issue with the way the fret ends have been dressed on the treble side, and you would need the best advice in the case of something like that.