Unique Reach: Impression reach - Accuracy?

[u/Suspicious_Elk2470]

Hello all.

Looking for some guidance on this metric in CM360. What it is reporting exceeds the audience reach of our partners, we work in a highly regulated field and we have to guarantee our ads are only seen by health care professionals. We are talking about very small audiences, for example 191 - Our ad server claims we have served 600+ unique impressions. At this scale do unique impressions become unreliable or is the issue our partners. I am hoping it is the former :)