Showing prospects historical performance of models

I have a prospect asking to see historical performance of our models vs. relevant benchmark (e.g., 60/40 model vs. a diversified growth with income benchmark). I'm with a large indy B/D. We use our own custom models which of course change over time. We also have YCharts.

How do others respond to this type of question, other than just dismissing it as a dumb question b/c things change over time, Fed put, etc?