Thanks for the tip but no, that's not it. I still get a fix -- it just takes much longer than with assistance data. IIRC deleting nvd_data was a trick that was supposed to help when you wouldn't get a fix at all.

When I first realised there was a problem with SUPL data I switched the GPS off, moved old /var/lib/supl/ad_cache out of the way and tried again. supld would then connect to supl.nokia.com but it wouldn't recreate or touch the file. When I restored the old file, supld would not touch it. Because I have two N810s, I also tried installing agps on semi-fresh device. It was the first time the device had agps stuff installed on it after reflashing it almost a year ago. The device didn't manage to retrieve assistance data either.

Interestingly enough now that I'm writing this, I realise that supld did in fact update the file yesterday. I've been trying to have supld to retrieve fresh data every now and then, even without a need to get a GPS lock. I didn't notice any satellite orbital data to appear, but that's what seems to have happened. It is not just the timestamp of the file either; touching the file manually won't update the timestamp agps-ui displays.