I mean... on the other hand, driver's job is to be trained for all possible scenarios including those you'll never even come across in your life, maintain the knowledge and skill at high standards at all times. You never know what you're gonna face just around the corner.
And at The OPC they test your skills, not your knowledge. If you've got the skills they're looking for, you'll be fine with the tests.
Also, really, you can keep the track of the tests you passed already yourself. This forum has already explained in much detail what tests are involved and which are to National Standard - if you passed them already, you passed them. If you failed any, you're gonna resit them.