But they believe this one, the oldest, cannot be cheated. It's also the one oath Aes Sedai respect both in letter and spirit.

Unlike the other, it doesn't even have the "DF" loophole.

Verin and Alanna could make exploding stones because each of those they needed to channel to make, and they had the Shadowspawn armies right in front of them. They knew none of those stones would kill humans, and they left none behind.

No Aes Sedai could delude herself that if she makes a weapon for others, there's no possibility that weapon will ever be used against humans. What if there are dreadlords or DF among the Shadospawn? What if the weapon gets stolen? What if one of the soldier is a DF and turn it against people? No Aes Sedai could make abstraction of all the possibilities and channel to make such a weapon.

Aes Sedai are limited to make weapons they operate themselves, and that leave nothing behind afterward which could betray the Oath.

That's the one oath which seems "full proof" in its goal of preventing the Aes Sedai from making weaponry for any war, and that's probably because it was introduced so early the Aes Sedai still knew how to properly design Oaths on a binder back then. Not only that, but the people themselves probably still knew enough to see the loopholes if there were any... It's the most restraining of the three Oaths, by a long shot. The second about not using the OP as a weapon is already less well designed, and the third and latest is largely a sham and PR stunt. The first Oath wasn't. It was genuine.