Interesting stuff! It's a little odd that gzip itself won't display (or sometimes even write) these values. Another tool that displays some of these values is file(1), at least with Debian's libmagic-mgc, for example:

  gzip compressed data, was "file.txt", last modified: Sun Mar  1 20:21:34 2026, from Unix, original size modulo 2^32 5

  gzip compressed data, extra field, has comment, last modified: Wed Dec 20 10:30:35 2017, from Unix

(weirdly enough, it doesn't show the actual comment string)