fuel filler problems

I’ve been in the automobile business all my life !! I’m 54 years old now ! Every slow fill or no fill situation that I can remember being involved with was due to a venting issues of the fuel tank ! Whether it be mechanical or electric !! Maybe one case there was an actual issue with the fill tube!! Guys I’m here to tell you I don’t know everything.. and don’t claim to !! But I don’t understand plugging a vent in the fuel system and at the same time having a slow fill problem that’s caused by a venting issue ?? So apparently than can be another issue besides venting ???