Gotta love programmers.
> So the question reduces to how much the type of compression matters here
If you compress, you can copyright the compressed bytes.
If you don't compress, you can copyright the uncompressed bytes.
As far as that copyright extending to derivations, e.g. decompressions, the answer indeed situation-dependent. For example, converting a copyrighted font from TTF to WOFF does not remove the copyright. But converting a copyrighted font from TTF to screen pixels to WOFF removes the copyright. (Sorry I don't have a reference; probably findable.)
The "self-extracting zip" derivation would probably fall into the latter category; that is, the copyright would not transfer.
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But even if the copyright were maintained during your advanced decompression, one could argue that editing down to very specific portion of that extremely large body of work was a substantive/transformational derivation, which they could then copyright themselves.
Transformative works are very common in art. The most famous example is Duchamp simply adding a mustache to a print of da Vinci's Mona Lisa, and copyrighting that. [1]
[1] https://en.wikipedia.org/wiki/L.H.O.O.Q.