I thought 30 seconds was automatically added on for each substitution?
I don't believe so. The '30secs per goal/sub' thing is something commentators came up with as an estimate for where added time comes from. It's not a set 30secs. Refs are supposed to allow for a reasonable amount of time at dead ball situations (goalkicks, throw ins etc and substitutions) etc, and only add on time if there are unreasonable delays.