Yes,

I renewed my permit to stay and new multi entry permit about 29 days before expiry. Hence they will issue the permit from the old expiry date. Went in and out before the old expiry date and was, correcty, given 1 years and 20 days valit to stay untill... the Immi guy said he never had given over 1 year but there are no issues as to the correct date

I donot think he gave you more than one year just that you donot lose any days on the old visa.

Believe what he is saying is his extension ended 20 Sep 2011 but he obtained extension on 20 Aug 2011 for period up to 20 Sep 2012 and a re-entry permit to the same 20 Sep 2012 date and then traveled and returned on 30 Aug 2011 to receive a permitted to stay until the 20 Sep 2012 date. (dates are obviously just arbitrary but show a return could get a date beyond a year in such a case).