If it says 6 are in stock, this means 6 to-go sizes are in stock. The spirit of the MX series is to have all the mixes in to go sizes, so we can quickly test, assess, and go on to the next.
Full bottles are actually made on demand. 
If someone orders a full bottle, we refresh the stock to reflect the amount of to gos available.
MXs are made in limited batches. There have been one or two exceptions where popularity took over and mixes were rebatched so othrs could join in the experiment. We’ve had SUCH highhhh super high custom order volume for the past few months that we haven’t had the capacity to release MX packs on the schedule we wanted. You should see our formulary book! Our MX series stretches all the way into the 300’s, but we don’t have the capacity right now to release them!
Once all the dust clears and we get new techies acclimated to formulating, we’ll probably release one or two new test packs per week.
In the meantime, if you have a google account, PM me and I can send you a formulation spreadsheet worksheet. Same worksheet we use in house to build mixes and MXs. It does all the mathwork for you, and you can send it in for us to make into an MX. (It’s fun! A few forum members have contributed MX formulas before~ When we use your formula or a variant as an MX, you get a $50 gift certificate)