Fireworks CS5 - no serial number?

Hi, about 3 years ago I bought a copy of Fireworks CS5 from a reseller who in turn sourced it from another supplier. I have a DVD, little product box with a holographoc sticker (& an 18 digit code) & emails with the tax invoice from the reseller.

At the time I had issues with the serial number & so only ever loaded it in demo mode on my old computer, did what I needed to with the program, put it in a drawer & promptly forgot about it.

Turns out (it would seem) that I never actually got a serial number or redemption code from the 3rd party supplier (who no longer exist) & the company who I actually paid the money to can't help, as they can no longer get the serial from the out-of-business supplier.

I have searched the "find your serial number" pages on Adobe's website, but they are not helping me. The closest thing I have to a serial number is a genuine Adobe holographic sticker with a couple of barcodes and an 18 digit code, which looks like it should be the serial number (but isn't apparently).

First question, if I don't have a real serial number & can't get in contact with the original resellers, is there anything I can do?

Note, please don't link me to Redemption code help or Find your serial number quickly ‌- I've ended up at those pages multiple times, but they do not help in this case, none of the numbers I have are 24 digits long.

Second question, if I cannot get my original serial number (the one I already paid money for that is), is there a (legitimate) way to purchase a new serial number for the Fireworks CS5 disc I have? All I want is Fireworks which is discontinued & I don't want a subscription, so would be quite happy with the version that I have - if I could get it to work.

Thanks for any help.