We use Nintex forms only.
I have recently gone into a form that does not have the formula I would have expected, is it possible to view any form of history for the form as to ascertain when this might have been changed?
in List forms You can use the version history:
I think for workflow forms You have to use the workflow history itself (open dialog in workflow designer).
Nintex Forms for Office 365 does not support form version history as of now. This feature will be coming soon as we bridge our gap in parity between both the products. Stay tuned for upcoming update announcements.