In some cases, we’ve used free external resources for our checkpoints and final products (ex: Illustrative Mathematics). In those instances, we’ve usually noted the source in the document, and you can find answers and discussion of the problems from the unit’s Backwards Plan. In other cases, we’ve written our own checkpoints and final products, and we don’t currently offer keys for them, nor do we have any supporting document that lines up specific parts of the final product to specific parts of the rubric.
For finding right answers we suggest collaborating with colleagues, using tools like Google and Desmos, or writing in to us with specific problems, if there are ones that are particularly tricky. We do recognize the importance of answer keys, and we hope to prioritize their development sometime soon.