Ebbie -

Each airline has their own interpretation of the rules. Some rules on carry on vs checked baggage can be rather arcane, and quite a few predate 9/11 but are more carefully observed now.

In addition each airport has it's own interpretation of the rules.

In addition, the inspectors at each boarding gate may interpret the rules differently. This set of rules especially may change when a new shift comes on duty.

In most US airports, it has been the practice to do all the inspections at central "boarding area entries," where once you've been approved you can proceed to the area specific to your airline. At these inspection points it doesn't make much difference which airline you're going to.

A few places have added inspection points you must pass to get into the individual "airline's area," and you may or may not get a clear indication from the airline of what their rules will be there.

A very few airlines then make an additional inspection for those boarding each specific flight, or may use the insepction at the "gate" in lieu of the one at the entry to the airline's part of the terminal. "Personal inclinations" of the boarding agent(s) and/or "what kind of nut the pilot is" may affect what they allow there.

Now if you want to know what the rules are going to be, you ask ...(?)

Also note that the rules may change at any time, so what they told you the day before your flight may not apply when you get there. Allow plenty of time to stop and read the current posted rules completely and carefully before you enter any inspection area. Then if necessary, you can exit and mail any "unexpected hazard" to yourself, and will only have to deal with the "port police" who determined that leaving the inspection point was "suspicious activity" under the current "terrorist profiling" standards.

John