You might be looking at an aftermarket mag. The original mags did have two types of metal followers and baseplates. You can look at some the auctions site that show them for sale and also check out the pricing. They are all-over the place for originals. $45-80.
The metal followers on the 39-2 mags were the early ones...mine all have metal bases and plastic followers from the early 70's. That has been my experience anyway.
I bought my 39-2 in 1969.
It came with 2 mags with metal bases and followers.
A few years later I bought a spare mag (pictured below).
It has a metal base and a plastic follower.
I reshaped the front of the base.