What the "door tag" notes and what the tire sidewall notes are two different, but related things.
The door tag used to note variations of tire pressure with "usage", as the owners manual used to note (i.e., smooth ride, minimal passenger load, no "trunk" load . . . or continuous speed above __mph . . . or "full rated load". Each type of operation had their respective recommended tire inflation pressure. The tag also listed the "minimum" tire size spec too, but not accpetable optional or "additional equipment" tire sizes (which caused some confusion in its own right).
IN the more current times, the door tag notes the factory recommended tire pressure for (apparently) the uses the vehicle can now "see". In more modern times, trailer hitch uses and vehicle loadings are not as widely variable as they were 30 years ago, by observation, which makes the tire pressure recommendation a little easier to make. This same pressure recommendation would enhance tire wear with a good balance of performance AND fuel economy, typically.
What's on the tire's sidewall is related ONLY to the tire and not the vehicle it's mounted on. If, for example, the vehicle recommendation is "30psi", but the tire sidewall notes a max pressure of "35psi", the door tag should be what is used, UNLESS there is a reason to use the higher inflation pressure--COLD INFLATION PRESSURE, not "hot" after it's run a while.
Also, consider the door tag as something of a "minimum spec" rather than a "max spec" (which is what's on the tire sidewall).
It seems that with the tire manufacturers and auto manufacturers working a little more closely together these days (especially GM as they have a complete group devoted ONLY to tire specs . . . the "GM TPC _____" spec number that you see on the sidewall of GM's OEM-provided tires). This would mean that provided tire tread widths are more matched to a particular rim width range so they'll wear better at the recommended higher pressure (a tighter range than what the rim width spec might be on a tire company's website spec sheet).
In the days when "32psi" was the max pressure for normal tires, "XL" rated tires (as in 6-ply rated P235/75R-15XL tires that you could order OEM on GM pickups in the later 1970-early 1980 time frame) went up to about 36psi and had a higher load capacity than the provided 4-ply rated P235/75R-15 tires.
I bought a set of Pirelli P77s one time. Their sidewall "mas pressure" rating was 45psi but were "SL". I asked a tire company phone rep about the load rating and why they had the higher pressure spec. He replied that the load rating was the same as at 35psi (for P225/70R-15), but the higher 45psi was there for "racing purposes". I thought that interesting.
In the more current time, though, there can still be some variables. For example, you might find better handling with about 2psi more air in the front than in the rear, to compensate for the more forward weight bias vs. available tire weight-carrying capacity of many vehicles, but not going below or above either the factory recommendation AND the tire sidewall's notations.
Remember that what's on the door tag is for that specific vehicle, yet the tire on the vehicle can be on many other varied vehicles that might NOT use the same manufacturer-recommended inflation pressure as where the tire might be now.
Just some thoughts,
CBODY67