That could be possible. I suspect there are also multiple "Potentials" out there who can Attune to a tool at the same time. I always had a suspicion that
this comic suggested that Sylvia was about to Attune to the Arkenpliers before the Volcano croaked her. The way she mentions its power to the recently-uncroaked Ossomer...
"Do you remember the sense of the divine? Did you feel that your hands were in contact with something greater than the world?" she asked. She turned her head and looked into the featureless distance. "The Arkentools were used to build the world. I wielded the Arkenpliers, and had the feeling that they could build more worlds than only this one. Their power was primal, undeniable, and very strange."
...suggests to me that she tuned in to their power far more than many other units could have. It's even possible (though unfounded) that there are varying levels of Attunement. That's the school of thought that says, were Stanley a Caster, he'd be able to wield the Arkenhammer more effectively. He may not have unlocked its true potential yet, given how much
more powerful the Arkendish and the Arkenpliers seem to be.
So it's possible that Olive found the Fourth Arkentool. As a Grand Abbie, she may have been able to comprehend that it held a connection to Signamancy, and decided that she had power over it. And, attuned or not, decided that made her its worthy wielder. Whether she then attempted to tap into Retconjuration, or whether she tried to use the Arkentool before it was ready and was summarily Retconjured out of existence, could vary. Hell, she might not even have tried to. If "Form = Function" for Signamancy, then perhaps her idea was to channel the power of Erfworld itself into Haffaton. Which would mean Haffaton's Signamancy would be that of Erfworld itself - in other words, she dispersed her side into the very form of Erfworld, the backfire causing her spell to have the exact opposite effect than she intended, and erasing them from existence.
But of course that's just my opinion.