If I remember correctly, some citizens in 600 A.D. say something to the effect that the Queen was found in the mountains. This means that somebody was in the mountains when she appeared, and they recognized her as the Queen.
I've also always wondered about why time seems to pass differently for you depending on the Era you are in. Perhaps Gates aren't connected in a 1:1 ratio. For example, for every minute of time the Gate in 1000 A.D. goes through, the Gate in 600 A.D. would go through 20 minutes. This would explain how Magus is able to ascend through the ranks of Zeal, which I personally believe would have taken longer than it does for Crono & co. to defeat Azala. Or why seemingly erroneous amounts of time seem to pass.
Bah, I'm getting off topic. Perhaps the Gate Key is nothing more than an electromagnetic wave generator. Just something to provide a reaction to the Gates. The Pendant is probably the same, in that a reaction with the energy of the Telepod causes the reaction, similar to metal in a microwave.
this somehow reminds me of the Dr. who episode entitled "The girl in the fireplace", where the Doctor and co. land on a 51st century ship. This ship also has something similar in commom to a Chronoverse time gate, namely the said fireplace, which is connected to 17th-18th century France. Now, time on the ship passes much slower than on the other side of the "gate", and Doctor & co. can literally see the years pass by.
In reality there's no way of knowing that time on both ends of a gateway passes at a 1:1 ratio at all, and since the time gates may not be 100% stable, then this time differential might change from one moment to another.
As a hypothesis on the necklace vs. the timepod, I have com up with this:
Most likely the timepod is made up of normal run-of-the-mill circuits. This most likely connects to the fact that ppl in 1000AD have fridges (they need circuitry to make sure the temperature i stable etc.). at least a part of the telepod MUST be some kind of a VERY powerful computer, since reassembling every single atom in an object correctly requires A LOT of computing power (billions to trillions of times the computers you use).
As you all may know an electromagnetic pulse strong enough can fry any given circuit in a computer. The dreamstone in the princess' necklace might have "enhanced" the telepod somehow. The Telepod has, as you all know, the ability to transport matter through space, but what if the "enhancements" from the dreamstone made it able to transport matter through time as well?
Now, if we look at Einstein's theory of relativity, space and time coexist in what is known as spacetime. The telepod might have ripped a hole in the spacetime as we know it, but in the process, it also ripped spacetime at nearby weak points in the fabric of spacetime throughout time itself, thereby creating the gates that the party travel through.
As for a more in-game theory, maybe Lucca took a shortcut while in the process of making research for and wile creating the timepod, she might have realised that the tecynology needed to evolve. This theory takes into account that we don't see COMPUTERS in 1000AD, so maybe she took the more "magical" approach by using dreamstone or another substance to enhance the already existing circuitry. The dreamstone/substance then reacted with the necklace, and the rest as we know is history.
As for the key, it must send out some kind of radiation or something else that make the gates (more or less) stable enough for safe travel. My guess is that by not using the key would rip Crono and co. apart if they were to travel through a gate vortex.