Looking for some help on manufacturer for my Grandfathers HO scale trains

Hello there, new to the forum. I wanted to reach out because I am having difficulty finding the correct manufacturer for my grandfathers train set. Its obvious with Kadee or Bachmann but a far majority dont have a visible manufacturer that I can find? I am only assuming what they are but want to be certain when I sell.

Hopefully you can help! Thanks

Very few companies sold freight or passenger cars without some marking under the underside. If you have questions, you can always post pictures.

Thank you for this information!