Perhaps this is at Sydney, but at UNSW, my abovementioned explanation is the way to go
. In the case of units that don't exist anymore, usually a subject replaces the subject instead of it being completely removed. In that case, the new subject is undertaken. But as I said, it may be different at Sydney.
By following a new handbook program, a multitude of problems can arise. For instance, say I were to have completed eight core subjects and four other Level 1 subjects in my first year as per the 2010 handbook. Then say in 2011, core subjects were changed to six only and that program requirements stipulated that I do a maximum of only eight Level 1 subjects. This would mean, if I were to follow the new handbook, that I have done two more core subjects and that I would have to repeat a semester because I have done more Level 1 courses that allowed. Clearly, not a reasonable expectataion.