To JWs, Mormons were wrong with their polygamy -- many wives for men. Of course, they ended that practice back in 1897. JWs don't tell you that it wasn't till 1947 that Watchtower began disfellowshipping those guilty of polygamy.
To JWs, Catholics were wrong when they required their members to avoid eating meat on Fridays. Of course, they ended that practice in the 1960s.
Doctrinal errors of other churches.
When JWs change their doctrines they are not doctrinal errors -- instead, they are NEW LIGHT!
Changed end dates -- even they have lost count.
Changed resurrection of the Sodomites -- you need the fingers of both hands to add them up.
Changed Superior Authorities of Romans 13. Changed "this generation".
Changed thinking of the Wild Beast -- discovered to have membership to a United Nations NGO.
Could there be even more?
Len Miller