Did you TELL your farrier he oversteps? It sounds like you didn't. That's not the farriers fault then.
As for 12 weeks in between- yes some of my horses have gone that long. My farrier was in a motorcycle accident and we had to scramble to find a replacement. It took over 3 months to find someone. No one went lame, no one was grossly overgrown. In my area a lot of people don't even trim over winter, I usually trim in November and then again they get trimmed in March, then every 6-8 weeks until November again. We don't ride during that time because its so nasty out and cold, and too much ice. If I had an indoor arena (I wish!) that would be different, but they simply don't grow very fast in winter.
Its not the matter of how long, its a matter of how his hooves hold up.
Spent a whole hour today laying in a pasture, waiting for a sparkling vampire to show up. Alas, I woke up and looked over, only to find a mound of horse crap. Sigh.