Total Unique Searches shown at the bottom of Summary usage report are also known as platform searches. 
Unique searches number should match platform searches on both Counter 4 Platform Report 1 and Counter 5 Platform Master report.

Subtotal Searches number is basically totaling up all searches shown on the left-side of the report. This may include cross searches of individual databases as well as searches listed next to any parent database. 
This may lead to an inflated usage search metric.

Explaining Unique Searches and Subtotal on Summary Report