http://www.mitbbs.com/article_t/PhotoGear/31251190.html
(in Chinese, Google translation to English here)
The following is a summary on what are told. Some are already well known but some are yet not:-
1. The 43 and 77 Limited lenses were designed by Mr. Hirakawa, Jun (平川 纯), who designed at least these lenses (which I own almost half amongst them);
2. The 43 was first marketed back to 1997, and was the first lens using the Pentax new Ghostless SMC coating design/patent and technology;
3. The Ghostless SMC was developed to fulfil the special need and application of the Japanese traffic police force for taking photos of the car plate of vehicles during night when the headlights were causing severe flares to the camera lenses such that the plate number could not be seen clearly in the recorded images;
4. The 43mm focal is actually the diagonal length of the 135 film, thus making it as the most ideal and perfect "standard" lens focal for 135 format cameras;
5. The 77 Limited was marketed in 1999, following the 43 Limited;
6. Pentax wanted to make the second FA Limited lens to a portrait lens but with a different focal and yet to be smaller than those standard portrait lenses. So, it had not to be a 85mm again. As Jun Hirakawa liked much the traditional Japanese cake made by the cake maker "喜月堂" whom has a logo of the Chinese word "喜" writing similar to three seven "七" Chinese words, he simply thought about to design a 77mm lens. Cited:-
http://www.246.ne.jp/~hirakawa/Limited/77yurai.htm
(in Japanese)
It is told that the teapot in the above photo was hand-made by the grandfather of Jun!
7. The three FA Limited was originally developed by Jun Hirakawa also. However, Jun prefered smaller lenses that should look more elegant. He originally designed a FA31/2.4, based on the optical formula of the old K30/2.8. However, the decision maker at Pentax/AOC didn't like that for some reasons but wanted to have a faster lens. Soon later, Jun was replaced by another two AOC optical designers to take up the project, namely, Mr. Ito, Takayuki (伊藤 孝之) and Mr. Murata, Masayuki (村田 將之). And they finally made the FA31/1.8 Limited lens;
8. The origin of the green lens-changing ball-mark:-
http://www.246.ne.jp/~hirakawa/Limited/fingerpoint.htm
(in Japanese)
It is all about antique, and is the colour of the Emerald material that used to make the world's first glasses and lenses.
9. Other explanations of the 77 and 31 focals:-
31mm is close to the diagonal length of the 24x18 movie film and format (which should be 30mm anyway, to be exact);
77mm is close to the diagonal length of 6x4.5cm film and format (which should be 75mm).
Read Also:-
Lens Technical Report on SMC Pentax FA77mm F1.8 Limited and FA43mm F1.9 Limited
Design and Construction of the DA14/2.8 - Leitz Lens Patent, Schott Glass (Not Hoya's)..
The Very Different Fates of Two ex-AOC Top Optical Engineers