Remember that every time you check your tires with a gauge you are letting out some amount of air. When you clip your pump onto the tire, if you have presta you'll lose more air.

When i rode mountain bikes regularly, i set my air pressure based on the trail i was riding. Some trails when muddy or super technical, i'd ride below the minimum air pressure.

I notice riding my road bike 700x23 i look down and think, mmmm i look like i'm low, ask Jen and she laughs and says you're tires are FINE.