Bava Batra 163 - Prevention of Document Forgeries
One empty line between the document's text and the signatures of witnesses is to be expected , but two make it invalid , because this opens up the document to forgery. The space of the two lines is measured in the larger handwriting of witnesses, and not in the smaller handwriting of the professional scribe. We assume that anybody who falsifies a document does it himself, and does not go to a scribe.
Rav said that a certified document with both its text and the signatures of its witnesses written on erased parchment is valid, if it can be discerned that it was erased only once. But maybe he erased the document and the signatures, wrote a new document, forged the signatures and re-used the certification? Rav answers that such a document is certified not from the certification written in it, but from the signatures, thus the forger gained nothing.
Art: Van Gogh - Drawing Board Pipe Onions And Sealing Wax