Lutz,
I now have had several comments back from tyre reps re you observation - and there are two sides to this story if the tyre is from a European based manufacturer then generally they will contain a lot less info than a tyre made by a Japanese or N American maker .
European manufactures tend produce their batches of tyres in working weeks, where as the Japanese tend to move more volume through the limited factories and so may produce two different types of tyre during the week or rather over a period of time.
Some companies like Federal use two different marks a technical one and an age one. Others like Toyo go for batches where as Goodyear/Dunlop use date but refer to the number in the trade as batch.
So in conclusion the words of the Michelin man (no not that one ) are probably the most correct - "we make it simple for the public to identify age as it's a key component to tyre safety"... yes your friend (I think he as referring to you lutz ) is the right, what is posted on the Web and in tyre distributors premises is designed to make the public consumer more informed
Sorry my reply took a while to come if you need any more info I'll get it for you
Regards