The reason York recomends checking the nail spacing on three trusses in a row goes back to the MSFH days. Unfortunately, one cannot always be sure of where the location of a truss in its relatationship to the sheathing (edge or field). By measuring the nail spacing on three trusses in a row you are assured of documenting and including both edge and field measurements in your inspection. I do understand you can look at the grain pattern on plywood a good portion of the time and will be able to identify an edge. That’s a lot more difficult on OSB. Anyway, by the time you do all that you could have likely measured three trusses and been out of the attic and used a good inspection method to boot.