madhum20 I'm guessing it depends on the counting methodology.. In past tickets we have seen partners counting only the new uniques in the last 30 days; ie: the new users we have uploaded for a specific segment in the last 30 days.
At the same time my understanding is that AAM is looking at the pool of users who are part of that audience in those past 30 days.
This is different and that would include users uploaded some time ago as well. For example The TTL on the constituting traits are usually set to 120 days so it would include users that were originally uploaded even 3 months ago but have had no activity since.
If profiles are not changed in a long time, they may be discarded by the destination
Wait for the rest of the community to chime in but I guess the above might explain the discrepancy or at least some of it.