See these little D rings? These pieces of hardware were added at the turn of the century. What do they do? Well, they make it easier for you to attach your strap.
These d-rings are also called zeros because... well, they add two zeros to your price tag. Kidding but not kidding. Kellys that have two double D-rings are a fair bit more expensive than their vintage counterparts.
But this isn't a bad thing. It means you can get a lot of great deals in the vintage world!