This bit seems strange to me. If you need a dating scan done, why wait until 12 weeks? It's more accurate earlier on - the difference in DS between 8 and 12 weeks was significant. And if you need a dating scan because you don't know your dates, and you do want the nt part done, then worrying until you think you're 12 weeks could mean you miss the window of getting the right measurement. If you know your dates and don't need a dating scan, and don't want the NT bit done, then why do the 12 week one at all?

For us, we only had two scans with DD - 12 and 20 weeks. With DS we had the dating scan because he was a bit unexpected and AF had only been back twice and was abnormal, then the NT scan, anatomy scan at 20 weeks and an extra one at either 32 or 34 weeks I think, just because he was measuring so huge. I nearly didn't do that one.
Yeah I wonder about this now too. I guess if you were really unsure of your dates and wanted to check you could get an early scan here. I think the reason is that in the Netherlands you tend to just go straight to a midwife and your first appointment is normally around 9 weeks and you then make the appointment for the scan which is done at 10-12 weeks. I think they make the 12 week scan part of the routine here to check for missed miscarriages, check for multiples, get a reasonable idea of dates etc without worrying too much about getting an exact date also for people who do want the NT test, so it's a kind of good compromise all-in-one early scan time.