ECL Codes, why so much confusion?

[Jeff H]

ECL codes do change based on combination and also based on prices/combinations. Just look at Jerry M's book on the 5 different versions of the 69 Z28 option during the year. The M21 codes vary for different reasons and the M40 codes vary for completely different reasons. Assuming you understand them is a bad assumption. M40 merely refers to turbo hydramatic transmission and the base engines got the TH350 and the high hp engines got the TH400 but they were both noted as M40 so the ECL makes a big difference. The codes vary from year to year and model to model so you can't even try to compare Corvette codes to Camaro, Nova or Chevelle codes. We're all trying to learn more about how GM built these cars and these invoices with the ECL codes will help us learn a lot more than we currently know. I think you completely misread the posts about it but if you know the different M40 ECL codes for 1970 then please share with us.