Oh good point. I guess it's possible then. Although I will point out that a majority (maybe all?) of the girlfriends have been to be revealed as such fairly quickly. I can't think of any that appeared, disappeared, then later became on of the GFs. But first time for everything, right?
Except for Mei I believe all of them were introduced and and Zinged in the same chapter.
Mei appeared first in
ch18, pg14 (though her features aren't more clearly defined till
ch20,pg21 and
ch21,pg12) and doesn't zing till
ch30,pg18.
But reporter girl hasn't shown up again since. Still a possibility though.
By amount of appearance she has less possibility than the demon vice principal "Baba An" who's eyes are always covered with sunglasses.
Shudder.
EDIT: Terrified at that possibility I actually had to go and check and her eye(s?) was visible in
ch12,pg4 when her foundation was melted by Kusuri's drugs, so maybe,
hopefully, not a candidate, unless she turns out to have some secret more normal identity outside of her demonic vice principal role (split personality?) and the single eye reveal doesn't count as eye contact needed for the zing...
On the subject of split personality, that would be a fun trait for a girlfriend.
One personality falls in love, but before they get to the kissing scene, and subsequent introduction to the rest of the family (or even after the first kiss and introduction!) she appears to have forgotten him (and the rest) and then
zings again. So that if she's switches in the middle of a situation, or because of a situation like embarrassment or some other emotion causing the switch, one or the other personality might find themselves in a love dovey or other odd situation all of a sudden
OR the second personality doesn't even fall in love at all! Ever, and may uncomfortably find herself in lovey dovey or other odd situations. But wants to support the other side of herself so tries to pretend to go along as well she can, but more often not pulling it off and being found out.
A similar multi-zing scenario could work with an amnesiac girl.
Meets and zings one day. Get along well and part for the day after school as Rentarou doesn't rush things if the girl isn't sure about progressing quickly.
Meets the next day and zings again. And the next day.
And again. And again.
At first she totally forgets him before they meet again, but with a nagging feeling left behind she can't place, until she meets him again and zings again and she remembers all her time with him after each zing.
Eventually her amnesia regarding Rentarou is cured and no longer needs to zing with him to remember their past interactions together and anything she does with/near him can mostly be remembered unlike she could do before, but her amnesia trait as a girlfriend could remain by still struggling with the other girlfriends occasionally plus other things in her life.
Got off track there...