We adopted a 3 year old JRT not too long ago from Morris Animal Refuge. They didn't know anything about his past other than that he was an owner surrender from another shelter, but I'm almost positive it was a similar situation - he's extremely reactive and absolutely hates kids and/or people abruptly getting too close to him, but is otherwise the sweetest guy. He's made a ton of progress in the short time we've had him, but I don't think he's ever going to completely change based on what he probably went through before this.