I saw your recent edit to the Theme Park series article, and I'd first like to thank you for following our guidelines. In regards to where to put the information, if it can be confirmed this edition of the game received a PC version (DOS, Windows 3.x, Windows, Mac, etc.), then that should go in the Theme Park game article under the availability section (see https://www.pcgamingwiki.com/wiki/PCGamingWiki:Editing_guide/Availability#Version_differences for that).
The "Designer Series" part, if that can be confirmed, would be a nice addition to the Theme Hospital article's introduction section, specifically the first part of the introduction section. It would need to be short, something like "known as "Designer Series" before release", as it doesn't pertain to any technical aspect of the game.