When using the getTreatment call, only some Impressions show in Split UI, when counting all the different treatments (on, off, etc.) the count does not match the records in the Live Impressions tab.
The Split cloud will de-dupe Impressions that have the same signature, to minimize the number of impressions created, here is the formula:
All impressions with the same split, treatment, key, bucketing key and rule within the same minute (or HTTP Post) are lumped into one Impression. This way the Split system can be scaled while maintaining a good representation of the treatments.
Based on the formula above, it is possible to get the same approximation of Impressions by counting the unique combination of split, treatment name, key id, bucketing key (if used) within one minute.
This will be an approximation to the count in Split UI since the SDK does not show which rule was used to calculate the treatment.