Add taxes date on invoice
A tax can have different rates depending on the date. Most of the time, the date corresponds to the accounting date because what is invoiced is related to this period or because the rate changes are not frequent.
But during a transition period where the rate is changing, it may happen that you have to post an invoice now but using the previous rate. For example, if you do a credit note for an invoice before the rate change or if you are invoicing services or goods that were done or delivered before the rate change.
So I think we should have a third optional date to define which tax rate applies.