You then have to decide how much you need to "fix" them. Unless they are hiring you to prepare files for them, I would not worry about anyone else's files and let them print how they print. If the magazine is unhappy with their printing quality and wants help making it better, it is obvious that they could use it, but not til they ask. I've been down that road way too many times. If they don't have a basic understanding of the color management, let alone color corrective, process, unless they're willing to pony up for a company wide retooling, I would not spend too much time with them. Make your own work look as good as possible and when they ask the other works sucks by comparison, you can tell them.
I would also take a test file, something with some known images plus a stepped gray and convert it using their press profile. Look at the total ink numbers. Look at the black plate and how far up the gray ramp the black runs to get a feeling for the k generation in this profile, then Assign the Adobe SWOP profile and see how much your file changes on screen. If the preview stays the same or only changes a little, then you can be reasonably sure that they are at least close to SWOP. If there is a drastic change in appearance, then you have to ask why that is, when the US magazine industry is getting fairly standardized.