Fronts Change. Rears Don't.
There are a lot of fallacies out there, but few are correct.
1. Remember the old saying “fronts change, rears don’t.”
This means as a puppy develops, oftentimes the front will change. Allowances have to be given for maturity and development as the set and placement will move.
2. Bad fronts are extremely hard to breed out.
Most experienced breeders will tell you sometimes it is best to start over in your breeding program.
The angles and degrees are only estimates and will vary depending on the function of the breed. Most all breeds that call for a “well laid back shoulder” conform to the 90 degree angle. This includes the Boston Terrier.
When evaluating the shoulders, feel for the bone length. Oftentimes a short upper arm will explain why the dog is moving the way it is moving.
Attached are three pages of literature. Familiarize yourself with a correct front end on a Boston Terrier.