All of my V4L cartomizers are indeed slotted, both very new ones and old ones...they'd have to be in fact to work with the new unslotted batteries...having said that the slot size and hole size in the cartomizers has changed 3x since ive been buying V4L cartomizers.
Steve will happily set you up with a slotted battery, your "unslotted" batteries must be new, that just started lately..3 holes and no slot right? i have heard of "4 holes-no slot" but don't own any of that variation yet.
Unslotted cartomizers??? no slot at all??? wow, didn't know that existed! Ive got some that i wish were slotted a little deeper...but i dont have any without a slot at all...theyre not greencig are they? lol
All the cartomizers I have had the factory modify, have slots, to varying degree's, I am still working with em to do the side holes correctly, along with the cutoffs, and get me higher end , litium ion battery's.
I have some samples here, trying to decide which I prefer. I think I can get the battery's working will all cartomizers, even w/o slot, in center, as long as side holes provide enough airflow.
Too bad I am not choo choo charlie, yaknow, he was as engineer

I am just a vapineer
Steve