The more I consider this, the more convinced I am that the Brewer's entry is a misprint. I haven't sent off my solution yet, so if anybody could get some clarification, I'd be very grateful. Or I could just get a life!
I've just noticed this thread (while looking for a Genius one; I've been on holiday) and although it is no help whatsoever I put tierced as not having a Brewer's had to rely on another list of heraldry terms I found which had tierced but not tiereed which would be a very strange word indeed. I would go with the misprint theory. Now to find some help with Genius.