After assigning credits to a client (within a membership or manually) it's possible to check when these credits were assigned, for what period, and when they were deducted.
In order to see a complete overview about this historical, you can head to Clients & Staff > Client's profile > Products
Now click on "Options" next to the credit you would like to check and select "View credit history"
Now click again on Options > Detailed Overview
You will be able to see when these credits were (or will be) assigned, when they will be deducted and their validity. Furthermore, in the "Notes" you can see with which modalities these credits were assigned or deducted.