Can never be sure...we are trying to re-construct the past here and some records and memories can be a bit hazy. Honest attempt any way. I thought you may have found a flaw with the chart (and some dates are a bit loose for the early models) but in your case how do you know it is a 1976 model. Is that what is on the rego? Is it a GT500, because they did not make T500s in 1976. Not unusual for distributors to sell off new old stock a few years later.