OP, it's very possible you had accurate pressures since tire air pressure changes 1-2psi avg for every 10degF.
Up der in Cheeseland, u fill dem tires up nice n plump when it's 0 deg out a couple months ago and they're good tires dontcha know, don't leak a drop of air, it's totally believable that they could be 10psi higher on that nice sunny May afternoon when you check them again.
Not likely the tpms is that far off. like my prev post, due to liability reasons, they need to make sure critical features are safe for the general public. They have. A vested interest in protecting their assets from the 10million sue happy consumers they serve every day.