It would have been about 3 years ago 🙂 Now not so much since you've got so many to go through. We did open up the download restriction on the final release for the ZD1000 (it's now EOL and no longer actively supported). I could open up the others, but it still won't help you as you need to get some versions that are tucked away in the archives.
Like virtually all enterprise network vendors, we do normally restrict access to software upgrades to customers with either active support contracts or remaining SW warranty (which is 90-days from receipt).