I read recently an interesting theory on the twelve tribes.
Do you have a reference for what you were reading?
It gets complicated as the Biblical account says Issachar was a child of Leah, but there is some evidence of the switching around of Napthali and Issachar. The tribes are always listed in the same order except for these two where one or the other may be placed first. The theory goes that a scribal error caused the changing around of their status due to the mix up in listing.
Some of the tribal lists are in different orders.
Gen 46: Reuben Simeon Levi Judah Issachar Zebulun Gad Asher Joseph Benjamin Dan Naphtali (12)
Gen 49: Reuben Simeon Levi Judah Zebulun Issachar Dan Gad Asher Naphtali Joseph Benjamin (12)
Num13: Reuben Simeon Judah Issachar Ephraim Benjamin Zebulun Joseph Dan Asher Naphtali Gad (12)
Num26: Reuben Simeon Gad Judah Issachar Zebulun Manasseh Ephraim Benjamin Dan Asher Naphtali (12)
Deu 33: Reuben Judah Levi Benjamin Joseph (Ephraim,Manasseh) Zebulun (Issachar) Gad Dan Naphtali Asher (10-13 depending)
Josh 13: Reuben Gad Manasseh (Levi) Manasseh Ephraim Judah Joseph Ephraim Manasseh Benjamin Simeon Zebulun Issachar Asher Naphtali Dan (Joshua?)
Judge 1: Judah Simeon Benjamin Joseph Manasseh Ephraim Zebulun Asher Naphtali Dan (10)
Judge 5: Ephraim Benjamin Makir Zebulun Issachar Reuben Gilead Dan Zebulun Naphtali (10)
1Ch4-8: Judah Simeon Reuben Gad Manasseh Levi Issachar Benjamin Naphtali Manasseh(again) Ephraim Asher (11-12)
1Chr12: Judah Simeon Levi Benjamin Ephraim Manasseh Issachar Zebulun Naphtali Dan Asher Reuben Gad Manasseh(again) (13-14)
1Chr27: Reuben Simeon Levi Aaron Judah Issachar Zebulun Naphtali Ephraim Manasseh Benjamin Dan (12)
Eze 48: Dan Asher Naphtali Manasseh Ephraim Reuben Judah Benjamin Simeon Issachar Zebulun Gad (12)