Early 911 attrition. How many are still out there?

[pkjense]

Hope sombody here can help me out wth a little research problem I am having.

I was building a spreadsheet (based on Excellence mag market data), and was supriised at the value rise on early 911s since 2002. This lead me to think, "I wonder just how many are left?"

So based on my car, a 73 911 T targa, I started doing some research. From what I can gather there were just under 3,600 of these cars produced as targas. That was 37 years ago! So I figured it would be simple to find the attrition rate, as I am sure the insurance companies use this information. Turns out, not so simple a task...

I found nothing porsche specific, so I tried sports cars in general. Nada. So I looked for a generic formula to calculate this data. Turns out Alan Greenspan did some interesting work in this field, but of course he concentrates on the domestic cars. This raises questions:
1) over 37 years would the calculations workout about the same for all cars?
2) would a car like a Porsche be more or less likely to fall to an early demise (smackatreeatitis)?
3) would they tend to have a longer lifespan due to higher quality, and owner pride?
4) One they reach a 'classic" age, would the attrition drop as they are used for weekend fun, when older domestics tend to get handed down to kids, or used as winter/rainy day transportation?

Greenspan (and others) seem to, despite some very complicated math, end up with an average attrition of about 6%. Anyone feel that applies to 911s? They also predict that at 12 years there are 50% of the original production run still in operation, and that at 15 years this figure drops to 30%. So, in the case of my car this would equal 1,800 cars remaining in 1984 and 1,200 in 1987. extrapollating forward this leaves us with ~500 cars in 2002, 400 cars in 2005, 300 in 2010, 220 in 2015, 160 in 2020 and 120 in 2025. If this rate continued (pretty loose science at this point), we would be down to about 25 cars in 2050 (like I'll care!).

If anyone has hard data to back this up or dispute it, I would love to see it. If it is true that there are only 300 of these cars remaining, than the price increases can be explaind almost soley on the numbers; sentiment, and nostalgia be darned!

My gut feel is that there has to be more cars than this out there. How do you support pelican parts based ona fleet of 300 cars? ;-)