Is there a difference between this and Fallout. I have Fallout Classic as well as Tactics and 2 but GoG says I don't own Fallout 1, 2 or Tactics.

These two versions are almost identical. The non-classical ones appeared as a Bethesda re-release. In the past the only difference was that the classical versions had support for macOS and more bonus content to download. I don't know how it looks today, but it's definitely not worth buying the newer versions if you have the classical ones.

There's one other difference:

Getting the newer releases will cause TES: Arena and Daggerfall to be added to your GOG game library.

The classic releases do not give you those two games.

With that said, if you already have the classic games and want those two early Elder Scrolls games in your GOG library, why not purchase a Bethesda game you *don't* already have? (Battlespire and Redguard are only $6, and you probably haven't played either game before, or you could go for one of the bigger name games, like Morrowind or Fallout 3.) (In other words, it's still not worth buying the newer version if you already have the older one.)

Fallout 1-2 Classic has Fallout Bible with its 205 pages, soundtrack by Mark M., and other things to download whenever you need. Unlike the re-releases, which only comes with downloadable manuals and installers.

Fallout Tactics included the soundtrack by Inun Z., artworks (70MB), Fallout: Warfare and other things, before the re-release. Now, your purchase only grants the game installer, and a manual.