One way of checking to see if only new users are using the technical documentation for a product is to check if there a correlation between the number of users reading the user documentation and the sales of the product.
For example, if the product is following the classic “Bell curve”, and users only need help at a certain moment in time, then the number of users should follow the same pattern. You should see a rise and fall in the number of readers:
Rogers' technology adoption curve
You can use analytics (and Web analytics in particular), to measure the number of users of any online documentation that you may have. If you don’t currently use Web analytics to measure your user documentation, then an alternative is to use Google Trends to see if there is a correlation between the number of people searching for help for your product and the number of product sales.
If you don’t currently use Web analytics to measure your user documentation, then an alternative is to start using it – today.