As NaturalMystic metioned, the original Delica (which we refer to as the Delica 1, but Spyderco never labeled as such) had an unlined FRN handle with a built-in FRN clip.
The Delica 2 (called that by Spyderco as well as by enthusiasts) was the original all stainless Delica
The Delica 3 (called that by enthusiasts, but just called the Delica Lightweight by Spyderco) had an unlined FRN handle with a barrel bolt syle metal clip.
The Delica 4 (called that by Spyderco as well as by enthusiasts) encompasses all of the current FRN with nested steel liner versions, as well as the current all stainless version and the new titanium/VG-10 damascus version.
Again, as has been noted, the Delica 4 has been in production for nearly ten years so, (aside from the bolstered damascus and jigged bone Sprints) it's the only one you're likely to find on dealer shelves.