Just to make sure I'm on the same page as you, you have an invoice that was already linked to an estimate prior to Feb 27 and now you'd like to link another estimate on top of the existing link between the invoice and estimate? If so, it's important to note that you'll have to create a single estimate for each invoice. However, the program does allow you to do this in reverse, which is having multiple invoices for a single estimate. This can be accomplished using Progress Invoicing. Feel free to ask to ask other questions.