The downside of the ECOdiesel is that the AVX trans was geared poorly and the engine gets overworked on the highway, even in 5th gear. Most of these were eventually converted to full turbo diesel with the addition of the LDA IP. The ACH trans would have been a much better choice for highway cruising but that's VW for you...lol.
If you have 5th gear that's great, some were allowed to run low on trans oil and the first to go is 5th because of its position on the 020 case.
According to VW there were 750 1991 and 47 1992 cars, that is if VW figures are to be believed. It's unlikely you will be able to find out how many were produced in a particular color though.
Based on the number of these that came out of the woodwork back around 2006 I don't believe the production numbers I quoted before but I've never been inspired enough to actually see if VW would provide anything different.
As for rarity, yes, I would say that a 92 ECOdiesel is probably rare but so is my pair of never worn Nike Air Presto from before 1989, but that doesn't really determine value. Something can be rare but if not desirable then it has limited value, like my Nike shoes.
If it was one of 3,323 original Porsche 914-6 cars that would be one thing, but it's one of 47 Jetta ECODiesel cars....so you can extrapolate from that just what rare means in this case.
I'm not trying to be negative, just realistic. It's not like any ECOdiesel is all that desirable. In fact it wasn't all that long ago that people bought them as projects and converted them to VR6 or 1.8T etc. I'm not saying don't take a shot on BAT or something like that, you might do better than expected, but I wouldn't get my hopes up.
Steve