Odd date stamp

[xylenol15]

I came across this strange WE 1500. As many of you know in the late 60s-early 70s the date and model stamp was moved to the narrow area between the ringer gongs. However, this phone appears to have the manufacture date listed to the day, whereas usually only the month and year is given. Did Western Electric experiment with stamping the full date on the phones during this time? I saw that they did that for the 1949 500 some of the other forum members have come across.