Major gemological labs can certainly identify a diamond's origin (mined or grown). There are many characteristics that can identify origin, and color or clarity is rarely used as the conclusive indicator. Here is a semi-recent study of synthetic diamonds from my company: https://www.gia.edu/gems-gemology/spring-2014-ulrika-hpht-sy...

You are right though, gem-quality synthetic diamond technology didn't come around for several decades after this mine started producing.

Last I heard for the grown diamonds it was only because the grown ones have perfect clarity and color which is never the case for natural ones. So the price goes up for clarity and color until it hits perfect then it falls back to synthetic diamond prices.

If a synthetic version is better then the natural version can you still call it synthetic?