The 3 slots were introduced a lot earlier than the examples shown. They first appear in the 1971 edition of the IPL and it only lists the 3 slot as an option. The 1982 edition of the IPL lists both the 3 and 5 slot versions (The 5 slot not being Illustrated).
The Indian Flash Eliminator is conformation of this as its known as the No.2 and the example shown is dated 1974. I guess India has paid England royalties for it?