The latest Oliver Heritage magazine has an extensive article on the 995 Lugmatic. Check it out, lots of good info. The number of units actually manufactured is quite controversial with most 9 series collectors however.
I believe the 990 is the rare tractor, just going with the fact that it seems that 995's, super 99's & MF 98's seem to be more abundant and come out of the woodwork everywhere. Tossing in 2 pennies.