Whenever you edit a quotation/an invoice, you can still access its previous versions. There are two possibilities to get an overview of these versions:

• You can open the quotation/invoice in pdf preview and click on 'Show history' at the top of the page.
  
  

• You can also find this history by navigating to the page of the contact/company your deal/invoice is linked to. There, click on the Files button and in this overview you'll find your quotations/invoices as well. Right clicking on a file gives you the option to 'Show history'.