Get the serial number when saving a Sales Order

Hello,

  I'm creating a Sales Order with transaction VA01, then from the menù "Extras --> Technical objects" I enter a serial number. When saving the Sales Order or before saving the Sales Order, I would like to carry out some checks on the serial number entered: is there any internal table or structure that can be read from USEREXIT_SAVE_DOCUMENT_PREPARE where I can get the serial number previously entered?

Thanks in advance.

Best regards,

Andrea