If they are related and the Bristol brand is a name shared between companies, they should stay together. Like Renault or Volvo, where cars and trucks are made by different companies, but using the same "brand".
But that seems a more complicated case indeed And Bristol being a city, it does not make clear if they really "share" a brand or both use the name of the city. Since they are not complete strangers, I think it is easier to keep both under the same make on the site.
Another edge case was this one: https://www.imcdb.org/vehicles_make-Fiberfab.html
The German company was founded by someone from the original US company, and since they shared some models under licence it is easier to have both listed as only make.

I'm wondering if Bristol should be split between cars and commercial vehicles:
https://en.wikipedia.org/wiki/Bristol_Cars
https://en.wikipedia.org/wiki/Bristol_Commercial_Vehicles

In fairness, the Tramway company and the Aerospace company were founded by the same person so possibly not as straightforward as I first thought.

Indeed, I'll split these.
edit: done
https://imcdb.org/vehicles.php?make=FSC-Star for the Polish company, since "FSC Star" was its full name
https://imcdb.org/vehicles.php?make=Star-Car for the US marque
https://imcdb.org/vehicles.php?make=Star-mc for the Yamaha motorcycles
https://imcdb.org/vehicles.php?make=Star for the UK marque

Thank you for the new updates on the site! Maybe next task would be splitting Star brand. It's a Polish truck manufacturer but also US and British car manufacturer.

Thank you very much!

Done, I created a new page for the Spanish models:
https://imcdb.org/vehicles.php?make=Avia-AISA
And kept the other one for the Czech models, since that make is still active:
https://imcdb.org/vehicles.php?make=Avia

Indeed, I'll do that as soon as I've a few minutes

Thank you very much for the updates antp. Now we have this option, it would be great to split the Avia brand in two, one for the Czech, and another for the Spanish.
It's obviously not urgent.
Thank you again.

Already since a few weeks:
https://imcdb.opencommunity.be/forum_topic-9976-94069-Forum_issues.html
but as long as your browser had the old style in cache you didn't see the changes

Hey, the forum site finally got an overhaul! Very nice.