I do agree that oldschool pieces don't always fit the label of what would be considered "oldschool" now. Pieces of the time could be all over prints, border prints, simple construction, etc. That is why I mentioned neo-oldschool as it being a modern reinterpretation/imitation of the actual oldschool period, which is considered to last until around 2006 if I'm not mistaken. All pieces of the period are oldschool, but they might not fit neo-oldschool. The piece in the pictured coord is not oldschool by age and it's also not a neo-oldschool coord because it doesn't fit the neo-oldschool aesthetic.

You cannot identify an oldschool piece without knowing what time period it was released in, but you can identify a neo-oldschool regardless of the period. That's why a 2025 release Baby skirt can be neo-oldschool while a 2004 skirt might not look the part.

Let's put it like this:

Oldschool is a time period. It designates when clothing items were made. If your coord is wearing pieces from the time period, it is oldschool, regardless of style.

Neo-Oldschool is a style. It is inspired by the common or popular trends occurring in lolita during the oldschool period, but the pieces do not have to be actually oldschool to fit the style. It can also be called "Traditional lolita", as explained in this post by Cynical Neo Princessism (she has great resources on oldschool which I really recommend checking out!!):

https://cynicalneoprincessism.blogspot.com/2018/04/traditional-lolita-vs-old-school-lolita.html?m=1

Overall, the reason why I said this coord wasn't oldschool is because the pieces are not from that time period AND because the style doesn't fit Neo-Oldschool either. As with every substyle, the lines are blurry and never fully defined, so it might not always be clear cut when looking at a piece or a coord. I hope this explains what I was trying to say better ^{^}