Look above the mag catch hole... no scratches from the mag catch dragging on the side. This has not been inserted into an AR-15. This finish rubs off easily. It is a spray on (or dip in) dry lubricant. You can freshen this up with a can of "moly dry lube" aka "dry moly". This is a common item in industrial hardware stores.
Moly lubes come in different shades, some near black, some silvery gray, but most are close or right on the original mag color.
I have seen NEW mags still in the wrapper that did not look any better than these. See the silvery area on the second picture? That is where these have been in the box, stacked together, and that area rubbed on the bulge under the mag catch hole of the mag beside it. Just jiggling and handling the box will do this.
Unless these mags are recoated, I think they are new.
See ajm1911's mag? A little cleaning, and spraying on new dry moly will make that well worn mag look new. It appears to be well used. A good refurb would be to clean and respray the body, replace the spring, and if the old black follower, replace with a green follower. Or leave the black in if you want, they usually work well.
As far as the tabs, it is normal to have a big glob of the dry moly smeared there.