pg_stat_activity extra Fields are NULL

Dear Members!

Windows Clients, PG 9.4 on Linux.
I used [PID + Client IP + Port + BackEnd Start] for unique identification
of a connection.
Every connection store it's unique connection info in a table (per
DataBase).
F.e:
"8574|195.12.4.3|50120|2017-01-01 08:12:15"

Yesterday I realized that BackEnd Start + Client IP + Port would be NULL in
a query.
I checked it and it seems to be access limitation.
Extra fields are on or off based on the account and rights.

As I see the logic:
- postgres (admin) can see everything (db1, db2, db3)
- db owner can see the connections on his db (user1 can see db1, but not
db2)
- other users can see only their connections (user_x can see his row only)

Rows are not limited, only fields are set to NULL for "non-accessable"
connections.

If I use the db owners only for the connections, the technic will works.

But if it is a "member of" kind user, it would break my logic to
uniqueness.
The actual connection can join his unique string, because everybody can see
himself.
"8574|195.12.4.3|50120|2017-01-01 08:12:15"
But in this wrong case the another connection can see only:
"8574|||"

So we know only that the PID is living, but we don't know it's same PID, or
it closed, and reused by a new connection.

Is there a way to we can read these extra informations by extra call?

Or is there any way to we can determine it's same PID or a newer (from a
different connection)?

The always visible fields are "datname, usename, pid, app_name", the extras
(creation time) would be NULL for non-accessable objects.

The appname is seems to be limited (I see it's text, but when I tried to
set it longer with an extra GUID, it truncated).

Thank you for all advice!

Best wishes
dd