Lisa--
I think that overswitching can certainly cause too much milk, and some
mothers are definitely so keen and worried (and have listened to people
about time limits) that they switch back and forth.

I have also wondered about tandem nursing and oversupply because I know a
lot of women (myself included) who experienced oversupply and very fussy
babies while tandem nursing. Could be an interesting research project.
Leslie Ayre-Jaschke, BEd, IBCLC
Peace River Breastfeeding Clinic
Peace River Alberta, Canada