Pre numbered labels are no good.
If you go back to do an annual test in say an office, most of the stuff will be there from last time. You simply test, re label the stuff from last time and update last times test record sheet.
If you have them pre numbered, then EVERYTHING has to get a new number and you have to start your test record sheet from scratch.
I gave up filling in the labels & spent some money with Megger Mark & got a seawards printer.........................why didn't I do it long ago.