To some extent it depends on what you put in the butter to make it a compound. For instance, truffles won't handle freezing very well.
But your average, run of the mill compund, like maitre d'hotel, lasts pretty much indefinitely. It's a sort of a universal, "good-housekeeping" recommendation to use anything in a home freezer within six months; but I imagine you could go easily go a year without losing much quality in a stable freezer.
I used to fold a piece of plastic wrap in half then roll up the butter, in effect quadruple wrapping it, and store it for about 3 months with no problems.
Never stored it longer as I tried not to prep too much too far in advance.
I agree with CC. Fat absorbs all kinds of flavours and aromas, more than anything else in the freezer. Besides, most of us grab a quick slice of compound better and put it back int he freezer wiht a less than perfect seal, thus accelerating the process even further. Did you taste your Merlot butter? How is it?