Dials were larger while the cases were made to be less of a focal point...
looking straight at a watch from the 60's, you will many times notice that not too much of the case is visible.
The "New Haven" was dated by looking at the style of the watch. Notice that the watches from the early 1930's still have engraved cases.
The dial and crystal go right to the edge and the lugs are smaller.
That fact should be obvious to ANY red blooded male.
Some companies (as with the Gruen Watch Company), even lost rocords to fire or other natural disaster. I am sure they had no idea that their timepieces would someday be collected.
There are several ways to get an idea of when your watch was made.