Here's a thought experiment. With an English style name, a name could be shown as either "Joe Bloggs", or "Bloggs, Joe".

So, given "Jan van Nierop", would you expect "van Nierop, Jan" or "Nierop, Jan van"?

My point is to ask whether the "van" associates more strongly with the surname, or could it be viewed as behaving like a middle name?

I suspect that if you are sorting the names, the N in Nierop would be a lot more significant than the v in van. In this case, I'd consider treating the "van" as a middle forename.

The nearest examples I can think of in the UK are Irish names like O'Connor or Scots names like McDonald. The practice here is to treat the prefixes as part of the surname.

Would entering "van Nierop" into the surname field cause problems?

I don't know of any way you can add this prefix/suffix field to the names. :-(

Thanks for your answer. I thought of this too of course. It would be a last resort. My question still remains however: can I add data fields in Thunderbird?