Not following you Zo.
The way to keep cost low is to never register the .5 release after the purchase until 12 is available and then register 11.5 which gets you 12 for free.
As Larry says, it's the cheapest path to each full release. Done that way, you never pay the full release price $99 .
By definition you are only ever on the full release which means you won't get the benefits of the .5 release until the next full release. I can live with that.