my .02
When you order a knife from a custom maker out of 3/16 when you get your hands on it there may hardley be a spot that you could mic out to 3/16. Why? because the maker's been doin' what he do: GRINDING on that sucker turning it from a BAR STOCK of 3/16 into a knife that at it's THICKEST POINT may still be 3/16.
Now if you order a Benchmade or a Becker that's 100% production and made by machine start to finish there will be lots of knife that are still the original thickness of the barstock metal. As there should be because nothing has touched it in the manufacturing process!
Now my SJ LE mics out to .197 spine @the hilt
1/4" = .25
3/16" = .1875
call it what you will, mine is .197
Ask any of the sheath makers that frequent these forums about the VARIOUS thicknesses that Busses actually are after being born in JERRYLAND

Hey we all know that in JERRYLAND the calendar only has 2 weeks in it!

so if the whole time space continuum registers FREQUENT anomalies in JERRYLAND then it shouldn't be too surprising the weights and measures suffer from these anomalies as well. For example, did you know that a CG NO weighs 17.5 oz and a Mr. MOFO LE 17.75 oz
So custom or production, I don't know, I just know that all my Busses were born in JERRYLAND and each individual knife has it's own personality and it will do EVERYTHING asked of it and come back asking for some more.