I think 70ppl is a bit high for 1990, I have a photo of a 18 year old me (taken in 1992) in Devon with a petrol station in the background showing diesel at 45ppl. It was actually around 70ppl in 1999 and still less than £1 in 2009.I think the DERVs didn't sit for long as they were bought by companys, and were also appealing back then for the XUD 11 excellent MPG (Remember it was 1990 so it was around 70ppl..) and high refinement.
Just come back from Australia where diesel was 80ppl, although could go as high as £1.20 in the outback & remote locations. My 2.5 XM runs happily on veg oil

All nothing to do with VIN numbers of course.