How many are left?, that is a good question, along with how many were actually produced?
Of course how many GTA replicas have been made? or will be made in the future? are complementary questions (okay fair enough not the question asked UlrichGTA)
Here are some thoughts to answering the question as narrowed down by Ken who asked is it possible to estimate the current population size (number left) of LHD GTAs using the estimate of the population size (number left) of the RHD GTAs.
Or was Ken asking can you use the RHD GTA sample data to work out the sample estimates of the actual population characteristics of total GTAs like destruction rates of the population of all GTAs, thus LHD GTAs?
You could argue they are two different populations LHD and RHD and they have some things in common, like decay rates or destruction over time. Or that they are one population of GTAs and we can use the RHD GTA data to work out estimates of the population of GTAs
Statistically you would first be trying to use an estimate of the decay rate (destruction over time) of RHD GTAs cars over time which gives you a point in 2017 with the final population estimate (number) of RHD GTAs and use the RHD GTA decay rate as an estimate of the decay rate of the total GTAs to give a final estimate of LHD GTAs in 2017.
Some of the know variables/constants are starting population numbers?, others unknown variables are reliability of cars and drivers skills and tracks and their conditions and other race cars etc.
If the variables that are used to describe the decay rate (over time) are the same for both then you may be able to estimate the number of LHD GTAs left.
In my opinion the variables would be too hard to estimate as there would be missing information and you would have to make subjective calls on drivers ability /ranking and track conditions and team vs private car preparation, tyre choices and the RHD GTAs participated in different races in different countries as to the LHD cars etc..
Another approach is to draw a time line of cars destruction.
The 50 RHD GTAs time zero let's say eg. after the first year X destroyed cars, produce a graph of all the RHD GTA cars for each year from 1965 year. On the vertical (Y) axis put the number of cars still remaining on the horizontal axis put the year.
Since not all cars were built at the same time, you have to consider the build rate adding of cars over time combining with the destruction of cars over time to give population size for each year, thus the decay 'destruction over time'.
Of course the decay rates of RHD and LHD cars may be the same if they are part of the same population and you can use the RHD GTA data as an estimate.
In the end you may just have to plot the LHD GTA decay rate and compare with the more complete data from the RHD GTA decay rate.
If the decay rates are very different then I would suggest they are two different populations thus survival rates will be different, so doing a simple percentage ratio of RHD to LHD may not work.
In the early 1980s Anders Ericsson (S) started a GTA Registry and in 1984 I helped him register a few North American GTAs. Concurently at least in part, Thomas Pippon (D) kept a GTA Registry. The Ericson Registry was turned over to Kris Hatfield (US) at some point.
In the 1994 Tony Adriaensens (NL) published "Alleggerita" that had a listing of GTAs and some infomation and he was able to draw from the Ericsson and Pippon registries.
In 2013 Martin Ubelher (A) published the Registry volume three of the three volume second edition of "Alleggerita" that published extensive information that was known about certain GTA's, GTAj's and GTAm's. Other known GTAs and sisters had just the serial number listed. That listing includes known serial numbers and their history if known up to 1981. Not all of those listed are known today.
Other GTAs have come to light since.
Tabuchhi has published a listing of the known built GTA serial numbers although there appear to be one or two others built by Alfa that Tabuchhi does not list but are verified in other documents.
There are also a few known forgeries stamped with duplicate serial numbers that have been presented as GTAs. There is one with an unpublished serial number that needs verification. There are some with questionalble looking serial number stampings that may not have been adequately explained to date. There is at least one documented case of a serial number lost because of crash repairs.
Attached are some photos of the finished result of the 5 year restoration of 775511, a 1968 Autodelta prepared GTA Junior Corsa. The car has been finished in the same livery as raced by its first owner, Gene Strandberg, at events including the American Road Race of Champions at Daytona in 1969...
Seeking C Sedan historians!
3 years has passed since I bought GTAJ (775511) from Dan Rapley and it is now only a few months from completion of its restoration in Australia.
Tim Doyle has completed the bodywork (a bigger job than at first sight as the car had a twisted front cross member). Vin...