OVR has 2 important components that contribute to the overall player quality:

• Stars
• Tiers

Stars represent a mandatory index and the player’s base quality, and the Tier increase represents the permanent increase for the key attributes of the player. 

Therefore, in case your player’s OVR is increased, without reflecting on the stars, this means that the boost was caused by the responding Tier.

Make sure to check out your player’s profile and OVR article to discover more about how to optimise his performance.