If you create a form with version 1 and publish it, then with version 2 and publish it, then with version 3 and publish it, Central will accept submissions built from versions 1, 2, 3.
When you do any kind of data export, Central and Briefcase will use the version 3 form definition. That means that if you had
fieldA in version 1 and then removed it by version 3,
fieldA would not appear in your export, even if some submissions have it. That data still exists but you'd have to do some manual processing to access it.
Central will accept submissions for any combination of
version that it has published and that has not been deleted. There are a couple of special cases which likely don't affect most people but that I will illustrate below for completeness.
If you create a form with version 1 and publish it then create a draft with version 2 (no publishing) and another draft with version 3 that you publish, Central will accept submissions built from versions 1 and 3.
If you create a form with version 1 and publish it, then delete the whole form, Central will not accept submissions created for version 1, even if you re-create the form with version 2.