This is something that comes up regularly in the higher level classes or with the more advanced students.
There's a point in training where sometimes we want to reward every response and every bit of effort. Error-less learning can be a good thing.... but if we're having to talk about maintaining criteria.... there are errors that are being reinforced!
Training a dog can be hard, because we do have to adjust our criteria to the environment. It's not quite like cooking where you do one step and then go to the next. We have to be aware of our surroundings and our learner's state and adjust accordingly.
But we do need to remember to maintain criteria...at almost any stage there are things that we do not need to be reinforcing any longer and it's important to keep the end goal in mind and it's important that we are constantly working towards that goal.