In a perfect world the published specs for bicycle components would be an easy, predictable way to put together a bike.
Having assembled bikes with Phil Wood bottom brackets since 1975 I can tell you that this isn't a perfect world!
I've frequently installed a Phil BB with the "proper" chain line dimensions on a perfectly aligned frame only to run into shifting problems with the rear derailleur!
Why? Because until Shimano brought out their SIS indexing system there were no REAL standards for rear axle widths and freewheel seating locations!
Shimano's standards became the industry's de facto standards for OLN widths: 5 speed 120mm, 6 & some 7 speed 126mm, 7, 8, 9, 10 & 11 speed 130mm.
That's great for hub widths but throw in varying freewheel widths and seating locations and you have an unpredictable mess!
That's the nice thing about Phil BBs, it's easy to adjust them to get everything to work smoothly!
In the end it frequently comes down to trial and error plus some amount of compromise - these are bikes not Swiss watch movements!
Chas. Colerich
Oakland, CA USA