Welcome to The Cove!
At this point, to continue flaying at subjects as though people don't know them well enough may do damage in a variety of ways:
1. Sends the message they are not well enough trained after all this time--perhaps a lack of confidence in their competence, ability to learn or caring.
2. Hints that perhaps the trainer is not performing well enough--why else wouldn't they "get it" yet?
3. Maybe they are feeling they are being preached to.
4. You are possibly feeling the training effort is futile and resent having to keep after it. It is
very difficult to train effectively when one feels this way!
May I be so bold as to recommend you stop training now?
I suspect you've hit a wall and there is something else afoot here. It may be time for some heart-to-heart talks with these production people, and learn what they really think. But be ready if they are brave enough, or angry enough to tell you what you don't especially want to hear!
The problem might be complex and festering like a deep wound that never got treated adequately, like an adversarial feeling in a patriarchal organization.
Or the problem might simply be untidiness in work procedures (written or not). You may need to do some 5-S and 5-W to solve some conflicts and reveal need for changes that actually address the problem and not its symptoms.
I have placed a paper about this in The Reading Room: When Employees Don't Follow Procedures. You might want to look at it before planning your next move.
I hope this helps!