Here's an extract from my mod records:
Manufacturer Model Serial Comments
Uniden BCD436HP 376z38000725 Install GMOUSE G28U7FTTL GPS, front panel 3mm status LED, install C1.
Uniden BCD436HP 376Z38000758 Install GMOUSE G28U7FTTL GPS, GPS power switch, front panel 3mm status LED, install C1.
Uniden BCD436HP 376Z38000820 Install Ladybird PA6, switch, & indicator light.
Uniden BCD436HP 376Z48001044 Install GMOUSE G28U7FTTL GPS, GPS power switch, front panel 3mm status LED, install C1.
Uniden BCD436HP 376Z48004863 Install GMOUSE VK16E GPS, front panel 3mm status LED
Uniden BCD436HP 376Z48006329 Install GMOUSE G28U7FTTL GPS, GPS power switch, front panel 3mm status LED.
Uniden BCD436HP 376z58003562 Install GMOUSE VK16E GPS, front panel 3mm status LED, install C1, remove faceplate.
Uniden BCD436HP 376Z58003643 Install GMOUSE G28U7FTTL GPS, GPS power switch, front panel 3mm status LED, install C1.
Uniden BCD436HP 376Z58006630 Install GMOUSE VK16E GPS, GPS power switch, front panel 3mm status LED
Uniden BCD436HP 376Z78001129 Install GMOUSE G28U7FTTL GPS, front panel 3mm status LED.
Some of the older serials that had C1 (and therefore I didn't install it) didn't appear to have been installed at the factory--the solder joints appeared to have been done by hand rather than machine. The pattern isn't clear enough to define a cutoff serial number where one can confidently say that higher SNs have C1, and lower SNs don't. Perhaps once more data is collected, the pattern or a cutoff point will become clearer.