All stereo recordings are not labelled as stereo.
It’s not printed “Single” on the packaging, but singles are still singles.
They print instrumental (even in Japan) but it’s rarely so, it’s karaoke / BGM / backing tracks / no vocals
etc.
This Tomorrow (instrumental version) you’ve added is not an instrumental version, it is a karaoke, a BGM, a backing tracks version, etc., they’ve just removed the lead vocals from the mix.
In the west is the same, actually, there are many original karaoke on single b-sides, like Roses Are Red (radio instrumental) that you can check there it’s a karaoke / BGM / backing tracks / no vocals (we can pick a name you prefer or the most common worldwide, if it’s not karaoke; like EP was chosen instead of mini-album), but not instrumental.
Here is a true instrumental: Love Story (instrumental version) (even if there were background vocals humming, I would say instrumental)
But obviously, there are two point of views that won’t agree.
So I think it’s really better to remove karaoke relationships and manage with what we have (instrumental, partial, remix).
Because when karaoke was added, instrumental definition should have been changed.
I’m pretty sure in old forum and/or mailing list, the definition of instrumental where it says it plays the lead melody by instruments, was shared.