Basically, the four wheel Thomas was the first ever Plarail Thomas & Friends engine to be released. It says on my box copyright 1992. Note that Annie on the box artwork doesn't even have her name, possibly one reason why they updated Thomas. I believe this Thomas was released for only a very short amount of time in early 1992 - mid 1992, until he was updated with the 2nd version, the picture you have posted is the 2nd edition of the Plarail Thomas. The copyright on my Thomas reads 1992 made in Japan, TOMY 1992.
And thank you! 🙂 Would you like to purchase it or give me a reasonable high offer?
Also to note, the Golden Thomas has four wheels too. This is most likely because they were made from spare over stock from the 1st edition Thomas. Maybe consumer reaction of Thomas not having six wheels for children made TOMY redesign the engine due to backlash - I can definitely say it was sold and its not a prototype because my box has a sticker from a Japanese toy shop on one end. Use photos above for referance.