It probably wasn't a late build car then.
I have owned over 10 '69 Coronets and still have 5 of them and all 5 that are left have varying build dates from very early which is September of '68 (red 318) December '68 (red 318) February '69 (still red 318) Late May '69 (blue 318) and early July '69 (blue 318).
I even have a late build 273 2 bbl out of a '69 Dart 4 door that is definitely blue (not red or turquoise) for comparison sake.
I have literally seen over 100 '69 model 318 cars in junkyards and car shows etc. that back this up.
BTW, there is a lot of other differences in equipment other than engine color during the model year run that i have noticed, but this isn't what this thread is all about.
