I thought that might be the case as well, but I asked them on their official Instagram account what the deal with the other 6 minis is, and this was their response:
"All 13 will be available soon as part of Series 1!"
Interesting. Well, at least we know about the codes and can avoid rebuying any of the Series 1A bags. Maybe in the next wave, the boxes will be entirely Series 1B? There's also a chance the the guy running the Instagram doesn't know for certain and the front of the bags could change. we'll just have to wait and see.
Another interesting pull from the IG is the image of the Pogs from before the line launched. it shows FIFTEEN unique characters! So at least 3 are maybe Series 2 previews or were cut from the line, i guess. Freaky Fullback, Wolf Breath and Body Blow being the three extras pictured.