Speedmaster '78 Case manufacturer

Can anyone here shed any light on the idea that the '78 145.022 batch's cases were made by a still unknown manufacturer? As far as I know that esoteric symbol on the caseback interior was only on the '78 batch. According to "Craft and Tailored" the manufacturer remains a mystery....... can the forums solve it? Here's mine ( i use a false bezel DO90 in order to keep the original bezel (DN90) stored away for safe keeping- for those that might notice its the wrong bezel).

Best and thanks to who can shed any light on the case manufacturer!

Scott