When you import a MIDI file into a Cubase project, you're asked to either create a new project to import into, or import into the currently active project. You cannot select multiple files in the first import.
The tempo will be used from the MIDI file if it is the first one (and the projects tempo track is empty). In sub sequent imports of other MIDI files, the tempo is ignored.
Moreover the imported file is always placed in the beginning of the project, regardless of locator and marker placements.
If you instead try to import tempo track from another project, the outcome is similar, only the existing tempo track in the project is discarded/overwritten.
The client may deliver midi files from notation software like Guitar Pro or their own demo/rehearsal projects. If you want to record and mix multiple songs in one project this is a huge problem.
So how do you import multiple tempo tracks or MIDI files in one project?
(manual tempo track setup is not a solution)