There are so many 'methods.' It sells books.
In the end, a child has to be ready.
It is not necessarily per age of the child.
AND, even once a child is potty trained or knows how... bear in mind that accidents and/or regression, WILL occur.
100% potty mastery... is never a slam-dunk 100% everyday perfect thing, sans mistakes.
Mistakes, will happen.
It is childhood.
Its okay.
Then, there is Night-Time dryness. This is a totally SEPARATE process, from daytime pottying. Night-time dryness, is not something that is physiologically/biologically attained nor mastered, until even 7 years old. So, even if a child is day trained, for naps or night-time, a diaper is still used. And is normal. And does NOT 'confuse' a child.
My daughter for example, was potty trained during her 2 year old age... but even at 5 years old, was still using a night-time diaper for naps and sleep. And this is normal. And per our Pediatrician.
Then, there are age related fluctuations, per accidents. At a certain age, they 'think' they can hold their bladder... but cannot hold it as long as they think they can. Thus, they may have pee accidents or poop accidents. Normal. Normal. Normal.
It being childhood.
ALL of my Daughter's Preschool, Kindergarten and 1st Grade Teachers, ALL said that kids at these ages have accidents. And at night they wear diapers. Normal. So then they have the parents bring in extra clothing/underwear for the child to keep at school. Normal.
A child's organs also has to be developed, enough so that they child can mentally 'know' their body's cues.