Alt + . = Charmap shows that the utility is working.
Alt + 3 2 1 = Ł (L with a line through it) shows that the utility is working.
(Alt + 3 2 1 = A would show that the utility was not working.)
Alt + 3 2 1 = L (L without a line through it) shows that the utility is working but the program you are typing into is only able to handle characters in the Windows character set. Notepad on Windows 95/98/ME is such a program, which is why you would see that behaviour.
I'm afraid there isn't any documentation beyond what you have read already.
I don't know what you mean by a "Unicode key" and I don't know what it is you are trying to do. Perhaps you could give a concrete example of characters that you want to type. Give a description of the character, and the code you are typing, and what happens when you type it, so I can follow what you are doing.