This baseplate has a dimple in it so it won't slide one way, and it looks like the crimps on the other end, the baseplate retainer groves are turned down, so it can't slide the other way. With the little button pressed in, it only slides about 1/8" either way. The crimped corners don't look as if it was dropped. The blueing is perfect.
My other mag is a stainless or nickel body with a blued baseplate, and it's rear square corners aren't peened over. Same baseplate with the dimple at the end.
So, somehow straighten out those peened over corners, and make sure the groove is opened up enough so the baseplate will slide out? I am swapping in the late model followers to make these 9 rounders like the 904/906 magazines.