What means the marking code below the part number of this IC?

[EFran.3]

I have this IC with the part number 3485EB, found the datasheet but it doesn't explain what this marking code below the part number (M2123) means. What does that mean?

[Tesla DeLorean · Accepted solution]

Assembly/Production Plant and Date Code

Looks more like MZ than M2

https://www.st.com/resource/en/datasheet/st3485eb.pdf