I holidayed overnight last night to check on regen numbers. I looked at a couple of teams and all of them have way less second nationality u18. The English teams do better (probably because they're researched better and have more accurate percentages)
Also all the players with a second nationality were always born in the country they didn't generate in. The French-Belgian guy at Genk was born in France, all the Australians at Dortmund were born in Australia and none the Ghanian, , Greek, ... guys at Arsenal were born in England. The Irish guys at Arsenal were born in England on the otherhand, but they seem to be the only ones at first glance. Which even if the percentages are accurate still feels off.
I can upload the 2038 save if the guys at SI feel it can help.