In the TRTH 12.0 User Guide V1, it says "A limit of two concurrent reports allowed to process per report template". Where as in the Best Practices and Limits Guide v 1.0, It says "Each user can have up to 50 extraction requests running at any one time"
Thank you for spotting this error, the documentation has now been updated.
Here is an extract of the corrected version (for the full version, see the Best practices and limits for Tick History 12.1):
In order to support consistent performance and optimize response times for the most users, Tick History applies the following request execution limits and queuing on a per-template basis, which allows for more granular resource balancing.