behavioral intent

Dear Forum,

I'm looking for advice on how to validate a measure of behavioral intent.
here's a simplified example: let's say that I did a study on 5 products - I sampled 100 people and asked them to state how likely they were to purchase each product.

Then, each of the products launched, and several thousands of units were sold for each product. Now, I'd like to know how accurate my behavioral intent measure is, so that I can use it as an indicator for future products.

Does anyone know how to do this?

The good news, I'm still in the research planning phase, so all options are open.