[sdiy] 27C512 not Eprom?

[Theo]

Hi list,
I just got a box with assorted NOS parts from a friend.
Among what is in the box are +700 ICs of what I expected to be Eproms.
Metalized sticker on top and part number 27C512, so far so good.

However under the metalized stickers are no windows to erase the ICs.
If not Eprom then what are these; Eeprom, OTProm? or ???
The full text on the ICs is:

AM27C512 -200PI
9751MBM BB
(c) 1986 AMD

Any ideas?

Thanks,
Theo