Aggregate data from 2 sheets with conditions

[virtuosok]

Hi,
Let me know if it's better if I post sample data on Google Drive as it's a bit complicated.
I have several tabs as follows, let's assume each has 300 rows with data. Tab Summary has names in column J (I deleted some of the sensitive info).

Then I have separate tabs for each study mentioned in column A above. Let's assume I have 3 tabs, named Pt1, Pt2, Pt3 respectively for PD001, PD002, PD003. They provide more detail about each site # listed in column B above.
These individual tabs go as follows, see site # in column N below => same numbering as in column B above:

What I would need please, is a formula which returns for each of individuals listed in column J on first screenshot:
- total # of screens (see column Q in 2nd screenshot) for each of the studies, across all assigned sites (see column B in 1st screenshot vs column N in 2nd screenshot)

Individual study tabs are having a bit different outline (I'll need to fine tune column IDs for each), and that's the main reason why I need a separate formula for each study...