> consecutive sequence for invoice numbers is a mandatory, legislated requirement (mercifully, gaps are generally permitted, with caveats)

That’s surprising. In Denmark gaps are not allowed. You have to account for all invoices and if you have an invoice numbered 50, then you have at least 50 invoices to account for.

It's nice when you change invoicing software, to be able to have gaps. For example, before Stripe is invoice <500 and Stripe invoices have >500. This makes it simple for humans to determine where an invoice may be located during the transition year. Further, it means we can plan the entire switch-over in advance, vs. only knowing the invoice number AFTER the switch-over. This makes a huge difference in internal communications to customer support, because you can let them know how things will operate once the switch is done. If you can't have gaps, you won't know how to tell customer support where to find new/old invoices until after the switch.

In the Netherlands gaps aren’t allowed either, and I’m surprised that it is elsewhere, as that allows to you get rid of unwanted invoices whenever you want.

However you are allowed to have multiple sequences, differentiated through a prefix, but all starting at 0. That’s what we recently did to switch invoice generation tools (we actually still run both of them alongside each other atm).

Of course you could still drop some invoices from the end when you do this, but I guess tax authorities accept that risk.

The prefixes have to be in order though. You cannot start a prefix with A after already using prefix starting with B.

> There are jurisdictions e.g. Germany in which a consecutive sequence for invoice numbers is a mandatory

Same in France. I thought it was a pretty common requirement.