Any inclusion of manufacturers should only be done if necessary. Otherwise it needs to be kept to the computer/model. There are essentially only two (and a half) cases where including a manufacturer name is helpful:
If the model name/descriptor is not unique on its own. Examples are
- numbers like 2, 64 or 400 which are rather meaningless without company (or family) name, here Apple-2, C(ommodore)-64 and Atari-400
- generic terms are used, like PC, in IBM-PC, EuroPC and Apricot-PC
If it is about a model of a specific manufacturer, distinguished from otherwise compatible machines, like when a question is about specific details of an Apple II or Spectrum clone (*1)
The 'half' one is about names that have become household names, i.e. when a name became independent of the company/Brand, like IBM-PC does stand for a whole linage of machines including even lesser compatible clones.
As a rule of thump, basic tags should be made the same way one would talk about that computer, so Spectrum, C64, Amiga, etc.
Examples were including company names is harmful:
- Amstrad-CPC - it'll exclude anyone looking for information about a Schneider CPC (*2)
- Commodore-Amiga - Amiga is not only distinctive on it's own, such a tag would as well not include all Amiga made after Commodore (*3).
- Sinclair-ZX-Spectrum - What about all clones and more or less compatibles, contemporary or later on? (*4)
The first example shows perfect the problems about being an international forum, and not a splendid UK-only venue, while the last highlights the effect of vastly successful machines with one leader and many follow ups. Each related but not really calling for a tab of their own. Including the company-Name without need will expel them and reduce usability.
Tags need to be as inclusive as useful. This is because our tag system isn't a Taxonomy with the goal to give each and every item it's own category to distinct them as detailed as possible (like in biology), but to group questions of related topics, being not too specific. It's usage is to allow someone searching for a question to narrow it down a search using rather fuzzy tags. After all, the regular search function does already provide a full text retrieval. So if a question (or answer) contains a certain part - like a company name, it'll be found anyway. Similar for model names. Adding synonymus tags doesn't add any value to RC.SE - except adding a long list of tags at the end of a question.
Adding a tag flood just to be 'exact' doesn't help, but damages usability.
I know it's easy, especially for IT Folks, to fall into a rush of detailed naming and classification. I got the same urge. Still its better to fight that and put usability above architectural finesse.
*1 - This is a narrow path, as such clones usually do not have (and don't need) a tag of their own due too little number of questions.
*2 - Yes, there are quite some old time CPC users whose English is good enough to read RC.SE and still don't know that they need to search for the Amstrad tag when it's about their beloved Schneider.
*3 - But given, Commodore is kind of a grey area here as later companies (and users) loved to identify themself with the name. Just think the TheC64 sales hype.
*4 - Fun remark here: In East Germany spectrum clones were made and even promoted by state media, but neither Sinclair nor the Spectrum name was ever used. Instead they mentioned the systems only to 'Industry Standard Compatible Home Computers' :)