Could bladder training actually work?

Yes it can: Biofeedback, when indicated works for some, provided they are old or mature enough to follow instructions. I do not believe infants can be bladder trained. They train themselves. The concept of infants learning to relax they pelvic floor and external urethral sphincteric muscles ; at same time increasing intra-abdominal pressure is ridiculous. Fortunately most kids work it out for themselves.