No matter how light the file might be, if you need 1000 units, that means you send a 1000-page file to the printer if you use Data Merge, that is not as efficient as sending one page and 1000 numbers to insert in the print stream, but to do that you need a plugin, which is what that page Bob directed you is leading up to. I've never used the program Harbs has mentioned, but he's a pretty smart guy and if he says it works well, I'd take a look.
Thanks very much for your prompt reply, which reassured me that I was on the right path. From having read various Help topics, I suspected that I'd have to use an Excel data source for the numbers. Fortunately, my knowledge of Excel was good enough to know about the drag and drop facility to create automatic sequential numbering, so the data source creation was easy. In the end, it was the mail merge (no surprises?) which proved a tad tricky, but I got there in the end. I've used MM many times and quite happily in Word documents, but for Publisher label format, it was of course a bit different. The important bit that I had to discover for myself was the significance of, after getting to the Print stage, going into Print options, to Publication & Paper Settings, and selecting Multiple Pages per Sheet (& in my case, also "Single-sided" cos my default of duplex printing had come up). But TA-DA! All is fine now. Thanks very much again.
2. Yes, The code should be entered using CodeBuilder. Where you enter it depends on how and when you want to trigger the generation of the next number. If you want to use a button, that works. And no, you don’t use 000 in the NZ() function. If you want to DISPLAY at least 3 digits with leading zeros, then you do that in the Format function. Note, though, you will need to change that when you hit 1000 POs. sequentially numbering in publisher