Paolo86cripple: I already bought the game years ago but GOG tells me I do not actually own it.
You had purchased the Interplay (classic) versions of Fallout 1 and Fallout 2 (which were delisted in December of 2013, due to ownership of the Fallout intellectual property having been transferred to Bethesda). With separate internally-referenced identifiers, the Fallout games (Fallout 1, Fallout 2, and Fallout Tactics) had been re-released in the latter portion of 2015.
Paolo86cripple: I have Fallout Classics in my library. Is there any difference between the version currently on sale and the classic ones? If that's the case, is it worth to repurchase the games?
The original (classic) Interplay versions (which you have owned for more than a decade) have a large amount of downloadable extras. The current Bethesda variants only include the manual (or, in the case of Fallout 2, the manual and reference card), and
do not grant access to the remainder of the bonus content. Please, refer to the two attached screenshots.
Aside from the Bethesda branding (visible when launching the games), as well as the lack of Mac installers, the only difference in which I can recall is that the Bethesda version of Fallout 1 has the high-resolution patch pre-applied. Of course, that same community-developed patch can be downloaded and manually-applied to the 'classic' Interplay version.
Rest assured; there is
no logical reason to re-purchase.