I think I lose a bit of buoyancy over time like you said but I am not 100% sure and I thought checking if I vent bubbles without wanting to would be good.
Analyzing video of yourself diving is always a good idea. Most of us can hear the drysuit venting, it makes a distinguishable sound. You will also learn to recognize the change in buoyancy which together with the sound and your trim makes you aware of suit venting without even paying attention to it.