The info about the watermark comes from my own personal experience. I own a typed, signed letter with the post marked envelope from Tolkien written on his Sandfield Road stationary to a little girl in 1964 (I was able to contact the original owner who stated they had lost the letter at Princeston University in the late sixties. I bought the letter from a seller who found the letter in a storage box at Princeton). The Basildon Bond watermark is clearly visible when held up to a light.