Issue with duplex scanning

ok like mine
so you can scan the front; save
flip your document, scan the back save
you will have two separate files that you can send piece by piece to the printer -> either two pages, or 1 page front and back

otherwise you can scan the front, flip to the back -> sign + scan the back <- save
in this case you will have front and back in the same file

attention
I recently had a case where a site (ants) asked me to attach a copy of my ID card
I attached my only "front and back" file, but they still asked for the back
I attached the same "front and back" file
well it didn't work
so I re-scanned as in case 1 to have two different files, one for the front only saved as ID card front the other for the back only saved as ID card back
go figure!
however, to print side by side, it is doable on the same side of the sheet, by changing format, either by placing both files in a word document, at least you can see right away if it fits or not...