Believe it or not, a basic Turnout Rail is now a Phantom Gem of Plarail.
Why would I joke in my research? Let me explain in detail:
In 1974, the turnout rail was first manufactured. However during the same year, the transition from slippery surface to sandpaper surface happened. This means that the slippery turnout rail (3rd rail), was manufactured for less than 1 year in 1974. The first occurrence of this rail could be from the initial print of the ひかりごうターンアウトセット or the single item, then sometime in the same year, the set and single items featured the sandpaper surface rail.
You can see the differences of the surfaces. The excavation of unopened slippery turnout rails are not found as of today.
Image credit to Mr. Nayuho.
By the way, I managed to win these in an auction today, just testing my luck to see whether I get the slippery turnout rail. The front one doesn't look like it, but I'm praying that the 2 behind are slippery rails.