Austrian 20 schilling banknotes - 01 Oct 86. Are there other dates?

I have 4 x 20 schilling banknotes from Austria (N#202270).  All of them have the same date of 1- Oktober 1986.  Are there other dates available?  Does anyone know why they weren't issued until 19 October 1988?

It appears that this is the only date for this denomination issued. As to why it was not released until 1988, I guess only the central bank can answer that. My guess (in general) is that most banknotes are printed in advance when current stocks are becoming low and new notes are only issued when the old stock is depleted. 

I don‘t know about the Austrian law, but for example contemporary Hungarian banknotes (their first issues) bear the dates when they officially became legal tender, although they are usually put into circulation the next year. See for example this press release: Upgrading the 1000 forint banknote | MNB.hu  There are also other countries which issue banknotes in a similar fashion, like Denmark or Norway for example.

So I suppose that this was also the case of 20 Schilling banknotes, maybe to give the central bank more time to prepare people for the new banknotes and also to print them beforehand.