The bigger factories like Triumph, BSA, Norton, RE etc produced very detailed workshop manuals or "service sheets",
I'd only half agree with that statement Rex.
Norton manuals have an all too common "return part to maker" for that stage of repairs.
So all the complicated or important bits are omitted !!
Haynes etc also frequently don't explain the complicated bits sufficiently enough for a satisfactory outcome. ?
Crank regrinds in particular often didn't include the all important radius grinding details - so reground cranks often broke.
And cam or follower grinding details - forget it ....
And pistons were often only covered in a cursory manner.
So various types requiring differing clearances were completely ignored.
Everything seemed to assume you were using utterly stock parts in pristine condition.
I'd think that whatever Excelsior offered was better than nothing.
A complete workshop manual it may not be though ...