[Heathkit] EV-638 / Heath HDP21A questions

[George KB2Z]

Gm all,
EV-638 / Heath HDP21A
Would anyone on the list have a Data Sheet for either mic?
It seems to be common knowledge that they are the same, but I'm confused.
On the eham website the review of the EV-638 has the freq. listed to 10kHz.
On the Heathkit Matrix it lists the HDP-21A as only having a response to 3kHz.
Can someone in the know please help me out?
Thanks in advance, George KB2Z