You really do have to wonder what they (assuming no one person has the power to make such a ridiculous
route system) were thinking.
Note that this map doesn't show all of the city-Raheen legs of some of the route variations - e.g. a service from Pineview might operate along the route of the 304, a 304a(E) or a 304a(H), it may actually be displaying "309" on the front of the bus and change this en-route.
http://www.buseireann.ie/pdf/1302277116-Limerick-City-304.pdf (note this seems to include most/all of the 304a, but does nto explain the 304a route variations E & H)
Are they trying to cover the entire city with one bus number?