Retrieve total allowed activations without custom fields?

Is it possible to retrieve the total amount of activations allowed by a single activation key without using custom fields? I know I can use GetFeatureValue, but that requires me to create a custom field and enter how many activations a product key has. I would rather just get the amount from the actual product key itselfbut understand if it is not available.

Is there a best practice for this?

Thanks,Arie