Sounds like the hole in the magazine that catch's the mag catch is a little off.
You could pull the follower and spring and insert the mag to see what has to happen. Person might be able to remove a bit from the slot and make them work.
I don't know that they are any different from early to late but apparently so.
In Memory of Paul "Dietrich" Stines.
Dad: Say something nice to your cousin Shirley
Dietrich: For a fat girl you sure don't sweat much.
Cue sound of Head slap.
RIP Muggsy & TMan
"If you are a warrior legally authorized to carry a weapon and you step outside without that weapon, then you become a sheep, pretending that JOCKO will not come today."