Some are suggesting that the typewriter used for the Aussie BC actually had a #1 to use and that whomever was typing the document used the real 1 for the 10th and then fell back into the old habit of using the lower case l on the rest of the document.
That comment is post #20 here with links to several 1960s era typewriters that have an actual #1 available for use:
http://www.freerepublic.com/focus/news/2307802/posts?page=4