Cops can't just raid your house with a mere seed purchase, but they sure as hell would add that shit to the list and continue watching your house, going through your trash and trying to get an informant pin a bag of bud on you so they know they got a strong case on you. They need 2 controlled purchases.
Just growing, a reasonable # of plants that is, without scales or being known for drug sells the cops they know your odds of getting off in court are good so I doubt they would bother unless you're in some small town, then this shit is like King pin drug dealing, making the news papers and shit all because a 400w in a closet with 4 plants.
I wouldn't worry too much, even for the cat who got the snag. You got plenty of time to tear all the grow shit down and just chill if need be. If the letter was seized in CO and you live outside of CO then you're good buddy. The authorities that seized the seeds sure the hell aren't calling up your local Barney Fife to tell them you had seeds on the way. Just ain't gonna happen.
If the seeds were seized in your hometown or county then yeah I'd tear all my shit down and just chill on it a bit, lol. But barring that I wouldn't sweat it, if shit is getting snagged in CO then GPS might have caught the attention of Uncle tax man or the Feds?
Edit: Actually I should say, cops will knock your door down like morons over some dumb shit like a seed pack but what I meant is that shit won't fly in court and will not stick if you pony up on a lawyer. Oh and never say shit, ever ever ever... Never. Except: "My lawyer can answer that for you."