it really takes *self-discipline* .... one way that might work is.... place each of your 12 quilts into it's own large ziplock and number them- 1-12...stack them up in order...then, when that extreme urge to start a new quilt hits pick up the one on top of the stack and tell yourself...as soon as I have this together I can start this new quilt....sit down & get it done. it may go quickly, easily just because you are inspired *looking forward* to the next new one.
or, set aside one day each week that you only work on the *stacked quilts*
or, when you enter your sewing room decide you will spend your first hour working on a stacked quilt- before you start working on the new current project.
so, there are 3 ideas -one may work for you