Notice that all five of these aspects can also be used to define a vintage style outfit. The difference between a classic and retro styled outfit is usually just in the details.
For example, in a classic fit and flair dress, the fabric is often subtle, and usually a solid. A vintage fit and flair might have a retro print, or vintage details that take it from classic to vintage.
Though of course there is a lot of overlap between the two. Notice that both women look amazing in their respective ensembles. The reason is because they both follow the five points of classic dressing, just the one on the left has kept a more modern look to her outfit, and the one on the right is more retro in her appearance.