ok so fuddles said we shouldnt be afraid to post - so if I'm wrong dont laugh me off the board please
I think a blown coat is when, usually following neautering, the fur goes a bit awol - fluffy, coarse and generally a bit scraggier.
Poppys coat changed dramatically after bneing speyed - so much so that we now clip her every 3-4 months to keep it looking sleek - although that said, her coat itself is in great condiditon, just a bit wild if left unclipped
jasper also developed a kind of 'flyaway' coat about 6 mths after being neutered - not coarse or scraggy, just sort of withery - if that makes sense.
Some dogs coats dont change at all though
(scurries off to google 'blown coat' lol)