This date code is from a type "3b" Parkette in "grey pearl-red veined" and I am confused as to what date it is, as, if it reads .23, that date is too early for either the pen or the date code.

If it reads .28, the date code would no longer be in this format, at least if I've understood the information I've gleaned from sources on the web. The obvious conclusion, and the most likely, is that I am confused and have misunderstood what I have read. In any event, I would very much appreciate elucidation. Thanks in advance.