This can depend on the instrument that is being triggered.
Some synth patches are designed to be ‘monophonic’, and will only play a single note at a time. Some might even allow adjustable ‘portamento’ or ‘gliding’ effects if notes are overlapping. If the instrument in question has patches that can be edited into a more polyphonic mode, then notes can overlap.
Just as an example…I have a number of Garritan libraries that work inside the ARIA player. Some of the included instruments can NOT play more than one tone at a time if the ‘auto-legato’ feature is enabled. In this case the instrument is set so that ‘overlapping’ notes will generate a more legato attack, with ‘adjustable’ portamento via CC messages. On this sort of track, divisi part writing over the same MIDI channel wouldn’t work.
Sometimes I load up a plugin with a ton of polyphony going on in fully polyphonic patches and notes just get lost (some get cut short, or don’t sound at all). I have to remember to go into that plugin’s settings and increase the total polyphony of the plugin, then I’m back in business.
I forget exactly how Cubase itself treats things if you have duplicate notes, with an overhang of the previous note (I.E. middle C overlapping another middle C)…if it sends exactly what is showing on the screen (two note on events, before any note-off), then I suspect its sound will vary depending on the instrument receiving it. A true poloyphonic patch will sound the first tone, then the second, then release the first, and later the second (so you actually get the tone playing twice as long as there is overhang). For a monophonic patch, it can vary a good deal depending on how it’s programmed to react to overlapping notes. I.E. Some plugins/patches might muddle it up by cutting the second tone short at receiving a ‘note-off event’ if you have overhang on the same note. So…sometimes it’s best to simply try different patches, or even different plugins if you’re wanting to use the long standing general midi technique of ‘overlapping notes’ to simulate ‘legato’ playing, but are only getting chop suey.
It’s not uncommon to load up a plugin/patch that just does NOT like overlapping notes. If that’s the case, the Cubase key editor does provide tools quickly and easily remove the ‘overlapping’. In contrast, it also has ‘legato’ tools to intentionally ‘add overlaps’.
I’m not at my DAW right now to provide a screen shot tutorial, but let me know if you can’t find it. If I recall correctly, the note length tools can be found in one of the tabs towards the left edge of the Key Editor window. There are also some things in the main Cubase MIDI menu across the top of the screen that can be useful in batch adjusting note-lengths. It’s also possible to ‘build your own’ low level ‘logic editors’ to do all sorts of wonderful and creative things with ‘note lengths’.