I'm happy to report that I just received a new DS1225Y-200+ NVSRAM from digikey, plugged it into the GQ-4X USB Universal Programmer (under Windows Vista), and got a clean write and subsequent read of linux-works' 2465B calibration .bin file image. This verifies that two DS1225Y-200 chips purchased from Jameco were not functional, and that my GQ-RX programmer works just fine. The next step is to take my nicely functioning 2465B, de-solder the aging DS1225Y, take that image, write it to the new chip, and install it - via socket - into the scope. Thank you again to linux-works and BravoV for all your help!
PS - In word of explanation: I decided to first buy the "Y" version rather than the "AD" version of the DS1225 given the initially frustrating attempts to write to the Jameco chips. I understand the "AD" chip would have a freshness guarantee, so to speak, given its first turn on would be at first write, but ... I decided to limit variables and take small steps by installing an exact replacement type. Now, once the .bin image is safely tucked away and the new "Y" is in, the process can be easily repeated with an "AD" version years down the line.