The GMH drawings for the 3mm thick spoked wheel was first done in 1972. They are not available for display or copying. They have some slight minor changes noted which didn't affect the visual aspect. So it was obvious they were already planning the change at that stage. Bridgestone would have then tooled up for production and submitted samples for approval. After that the wheels would have been produced, shipped and installed. As to when the older stock ran out and the new ones installed it is probably not noted anywhere these days. In regard to previous requests the factory is definitely not interested in restoring any older wheels regardless of colour or thickness. They manufacture NEW wheels according to customers orders.