m40 helmet question

[HoundsTooth]

thats interesting i have a m40 hkp 66.
this helmet is a m40 hkp 64.
but what i found different is the fact the hkp stamp is on the side not the rear.
my helmet is a very low lot number so would this be the last of the m40 batches befor the change to the m42. ?

Have a look at the lot number spreadsheet on Frank's site:
https://germanhelmetvault.com/
It will give you a good idea on lot numbers.
Nick