The 12.841m is the total shorted on the ASX - all up total at that day was 23/04/15.
The number that have to still cover (buy shares to pay back to the lender)
http://www.asic.gov.au/Reports/Daily/2015/04/RR20150424-001-SSDailyAggShortPos.pdf
This total is about 4 days delayed. That is, the latest figures are for 4 days ago.
The 305k is the number for that day 28/04/15
http://www.asx.com.au/data/shortsell.txt