True the air pump supplied does change by 5 lbs on removal, Therefore you pump up to 80lbs (5 lbs more) and then remove pump valve to have about 75 in shock bladder.
Then when you reconnect the pump right away you should see 75lbs. This will verify how much your losing. You can repeat this test several times to check accuracy.
I had a leaker I couldnt find. Went in for service for a 19 chieftain DH and they put a new shrader valve and said try it.
Nope it lost roughly 25 lbs in 200 miles or 1 day. So I returned to dealer for replacement.
The replacement shock assembly now holds air decently about 5-7 lbs a month.
To be honest no air shock will be leak free. But shouldnt lose more than few pounds a month with all conditions being same.
In other words if you check it after a ride the shock is warmer and pressure is higher and in lower temps say wherever the bike is parked determines a pressure difference.
All air bladder vessels leak a few lbs over time but to leak 10 or more lbs in 200 miles could be considered as excessive in 6 days.
Any air shock seems very practical but real world conditions dictate different.
Dont know how much warrantee if any you may have but keep an eye on this checking with same temps like next day after ride.
Just like tires the pressure will go up some after riding.