I believe all
Core watches are created more or less equal within a certain error margin. I don't see why they would differ so much from one another. I'm also convinced the airport's instruments are way better than our watches in every aspect (quality, precision, sensitivity, etc.). Those two facts put together should explain why there are little differences in our readings and what the official reports say.
Last night, I did a little experiment on my way to work. I checked on Google Earth the altitude of my home (19 m) and that of my work place (44 m). I went to the bus stop and set my
Core on altimeter and the reference altitude at 19 m. About a minute after setting the altitude, it went up to 20 m and stayed there. When I arrived to my work place, it indicated 45 m. I suspect that extra meter was due to a change in pressure but I'm not sure. It could also be simply because of my height, my watch is at 97 cm from the ground when I'm standing.
While at work, I set my watch back to barometer and the reference altitude to that of the airport (35m). When I came back home, the air pressure was 1 hPa above that from the weather report and 0.10 in Hg above that of the airport.
Seems good to me.