A liquid class assumes the world holds still. The instrument runs the exact sequence it was given, so if the liquid behaves differently today than the day the class was built, the class has no way to know. Several of those differences come not from the liquid but from the room around it, and they are easy to overlook precisely because they are invisible.
Temperature
Temperature is the big one. Viscosity, density, and vapor pressure all shift with it, and a change of only a few degrees can move a validated class off target. A class built in a warm room can under-deliver or over-deliver in a cold one. Develop classes at your normal lab temperature, control that temperature where you can, and record it with the class so a discrepancy later has an explanation.
Humidity
Humidity governs evaporation. In dry air, small volumes lose measurable liquid to evaporation before they are even measured, which reads as a short-fill, and low humidity also raises static that can disturb low-volume work. Humid air evaporates less because it is already near saturation. Either way, the smaller your volumes, the more humidity matters.
Atmospheric pressure and elevation
Atmospheric pressure changes with altitude and weather, and it is tied to vapor pressure and off-gassing. A class validated at sea level is not guaranteed to hold at six thousand feet, where the lower pressure changes when a liquid begins to off-gas. If you move a method between sites at different elevations, re-verify rather than assume.
Vibration
Vibration mostly shows up as a measurement problem. It can shake droplets loose and it disturbs an analytical balance, so gravimetric verification wants a still bench. If your numbers are noisy for no obvious reason, the environment around the balance is worth ruling out.
The instrument cannot see the weather. If the conditions a class was built in have changed, confirm the transfers again before you trust them.