Overview
History of Mazinger Z on the Internet Archive
Most streaming services carry Shin Mazinger Z (the 2009 reboot) or Mazinger Edition Z: The Impact! They rarely, if ever, carry the original 1972 broadcast. Furthermore, they never carry the ancillary media—the soundtracks, the radio dramas, the model kit instructions, the laserdisc box art. Mazinger Z Internet Archive
It is important to address the elephant in the room: copyright. The Mazinger Z Internet Archive operates in a legal twilight zone. Toei Animation and Dynamic Planning (Go Nagai’s company) still own these properties. They have, on rare occasions, issued DMCA takedowns for specific files.
Note: The Mazinger Z Internet Archive is a fan initiative. To support the official release of Mazinger Z media, purchase the "Mazinger Z: The Impact!" Blu-ray box set or the "Go Nagai World" digital manga collection. Mazinger Z (Internet Archive) — Review Overview
Movies and Spin-offs: The archive includes theatrical productions like Mazinger Z vs. the General of Darkness and episodes of the sequel series, Great Mazinger. Vintage Ephemera : Curated uploads often include VHS rips of Tranzor Z: The Movie
The strict answer is: It depends.
Keywords used: Mazinger Z Internet Archive, Mazinger Z, Go Nagai, Internet Archive, lost media, super robot, mecha anime, photon power, great mazinger, grendizer, archive.org.