Dear Jarcek!
Thank you for the help. It seems, that you suppose that there is a mistake: instead of "letters" there should be "characters". At least your suggestion of the link clearly shows that there are no letters, that can be seen under 4x magnification on these coins. The one site, that you cited, that is
http://www.linguanaut.com/chinese_alphabet.htm
really explains the writing Chinese with letters. Obviously, every numismatist knows them very well and we don't need any external link to prove it, for the local Authorities indeed write Chinese with letters on coins and banknotes for illiterates (such as beginners and tourists). See both images of a recently struck coin, which is the excellent sample of it:
http://www.delcampe.net/page/item/id,366630346,language,E.html
No, the Numista catalog means real letters, not the Chinese characters.
It is clearly shown in the first post. Have a look, let's take your point of view and suppose, that the word "letters" means "characters". Then we oblige to conclude that in the 3id link of the first post for 1976 there are 2 types of characters. From the link in the link of the second post (we can not use the link in the 6th post anymore, for it describes some fantasy, we are speaking about catalog, that is, we need reality) it comes, that indeed there are 2 mints that make coins with different styles of characters. For the coin in question there is only Shanghai production (see the image of a real coin
http://www.delcampe.net/page/item/id,366629657,language,E.html that verifies this statement).
Now we have a contradiction: in 1976 there was just one mint, it means there is only one style of characters. The Numista catalog describes:
1976 Modern letters
1976 Stylized letters, different font
It means, that the 'letters' are not 'characters' and have nothing to do with legends in Chinese on coins.
That is why this post was created. Where are the letters in question? I still can not find them.