How many different ECU firmware versions are there?

[ZB911]

I've been looking all over for information that could tell me how many different ECU firmware versions there might be in total across all 96-98 993's.

I'm involved in a research project on OBD2 that could potentially benefit a lot of 993'ers with SAI-related emissions problems.

The workaround I stumbled upon is legal, toatlly free, easy and non-invasive. I was able to pass my 97 C2S with known SAI faults this past July using this technique.

The problem is I don't know if it worked on my '97 because my ECU firmware is "unique" in some way or if most or all 993's could be expected to behave the same way. A firmware version/VIN lookup table would be best, but lacking that, even any info as to how many versions there were (one for each year, 10 , 20, 50??) would be useful.

Any help is much appreciated.

Thanks, Jay