There are probably a full 12 piece mold of unnumbered 1x6 with large stud recesses. I've not found any matching patterns with the later numbered version. At least 4 different mold members exists, based on the bottom patterns. Without more samples I have yet to determine if the unnumbered 1x6 and 1x8 bricks originate from one common mold, or if each brick type had a separate mold. As for now, all samples are registered on the first mold member, as I haven't been able to differentiate the samples yet.