There are different formats for wheel dating in 1968. The first picture is an indication of one format typically used.
The rim face and the actual outer rim usually are dated separately. The first wheel picture posted the inside face is dated "12 67", while the rim is dated by the valve stem hole.
The date of the rim will be the one by the valve stem hole. So, as an example "1 26" is January 26. We can assume that's 1968 based on the date of the face (by the lug holes).
I would say a January dated wheel is appropriate for a Feb, March or April built car.
I think the wheels with a small "K 28" by the valve stem are after Shelby production.