Does anyone know if GTD had a date code system? I have some GTD taps and dies, and each has an alpha-numeric code on them. For example: X12, B9, C5, A10 HE, E3 HE, TT I1, D1, I6 HQ, HY Y2, G11 HQ, G H3 S12 HS GQ, Z2 HQ
Is there a method of madness for these codes?