I've never had any problems with surplus mags using black or green followers except for dents hanging up follower.  Think it depends on condition and abuse before they hit the civillian market and running semi or FA.  Only ever had one Cooper I recently sold but it tested and ran fine.   I rotate a couple Sanchez mags one with black and one with green follower in my shooting bag with no failures.  

Most all the surplus mags that hit the civillian market have had an issue at some point in time the main reason they were dumped.  I used to get them from local National Guard when they deemed as junk.  I went through them same as I do even when purchasing new mags and never a problem.  Disassemble,  clean, inspect,  repair, lube, assemble and use.  I even made a couple tools to remove the dents and 9 out of 10 times they are fine shooting semi auto.  If running FA buy new quality mags!  Apologies on jack as I have nonthing to add to OP weld question except I don't own any of those.