I agree you should take Edmunds' numbers with a grain of salt - they tend to be extremely pessimistic about European cars, for example. They probably also figure on your replacing tires, batteries, etc with OEM. They don't say but they might be taking repair costs somewhere else off the distribution than the mean or median to produce a budgetary number.
Also, are you going by age or by model year? Understand that the TCO they give is for the next five years, as if you bought that model year used now.
You could just have a car whose repair costs vary a lot.
The problem with your data, given your use case, is that you can't really compare it to anything but more of your data. I'm sure if we could see how the sausage gets made there'd be plenty to criticize on Edmunds' TCO calculator but it at least provides a way to compare different new and used cars, and it breaks down the numbers in ways that allow you to work with them a little - or compare them to experience - if you are skeptical. It's also not too hard to do a similar model for comparision for different use cases (driving only 5k miles per year brings your TCO on a reliable older car way down, for example) - you'll have your own estimates for each line item instead of their data - if you want to compare against their numbers as a benchmark.
Also, are you going by age or by model year? Understand that the TCO they give is for the next five years, as if you bought that model year used now.
You could just have a car whose repair costs vary a lot.
The problem with your data, given your use case, is that you can't really compare it to anything but more of your data. I'm sure if we could see how the sausage gets made there'd be plenty to criticize on Edmunds' TCO calculator but it at least provides a way to compare different new and used cars, and it breaks down the numbers in ways that allow you to work with them a little - or compare them to experience - if you are skeptical. It's also not too hard to do a similar model for comparision for different use cases (driving only 5k miles per year brings your TCO on a reliable older car way down, for example) - you'll have your own estimates for each line item instead of their data - if you want to compare against their numbers as a benchmark.