Hello,
Yes, it should be possible to find the information about the "original quantity" when the order gets archived (this can still be different form the quantity which has been entered in the very beginning - but this can also be seen in the archive - that's why we have the archive - to keep the different "versions" of an order).
For now this would be on an individual base.
But I also think this is a good candidate for a "product suggestion" ... to have the chance to get this done in the standard package and make this individual change obsolete on the long run.
experience.dynamics.com/.../
search for the application "Dynamics 365 Busines Central" and then add your suggestion / vote for an existing suggestion.
Depending on the number of votes for the same suggestion this suggestion gets populated and further discussed.
Kind Regards