Color is easy in this regard: E-6 is E-6 is E-6. C-41 is C-41 is C-41. It is black and white that is the problem when it comes to mixing films in the same processing batch! Color films are designed to work in a standardized process. Black and white films are not.
Sometimes I wish black and white had a standardized process. That would have made it easier for sloe learners like me to figure out the process
"I have captured the light and arrested its flight! The sun itself shall draw my pictures!"