Its a good bet its rust in that mess to.....bleaching it for 30-60 mins can help....but its a bitch and it smellllllls....I did it at one huge reset of a toys r us.....everyone of us got sick on that job....from then on out....no bleaching unless they want to $$$$$$$
so yes it will fade over time, but wont all be gone.....plus if the traffic pattern changes wellll then that tile has been walked on less as well....
also remember VCT as a general rule is porus, so depending how long that shelf was on the floor, and how many strip jobs.....thats a lot of time soaking that crap in..