Adding to the conversation,
From Bob Mannel’s book Small Block V8 1962-1969. On page 7-31, Figure 7K11 has annotations for two photographs of York compressor tags with date codes of 027K and 047:
“The first two numbers defined the month with the third number indicating the year. The trailing letter had no date significance. For this date code [027K], the date is February 1967. The (other) tag’s date code is 047, which decodes as April 1967.”