I've got one of the infamous BOE NV140-FHM N-41 panels from an ebay shop, which doesn't work with the FHD Mod PCB, but run fine in the T440 / T450.
As I have both T420s and T440p at hand, I tried to figure out why and had a look at the EDIDs of the NV140 and the FHD Mod PCB (which probably is the EDID of a AUO B140HAN01.x) using the tools get-edid and parse-edid from the read-edid package under Xubuntu 17.10:
NV140FHM-N41 EDID wrote: Section "Monitor"
...
DisplaySize 310 170
Gamma 2.20
Option "DPMS" "false"
Modeline "Mode 0" 147.80 1920 1968 2000 2200 1080 1083 1088 1120 +hsync -vsync
EndSection
If you look at the "Modeline" lines, you see that both screens differ in dot clock, timings and the polarity of vsync. I'm not sure about dotclock and timings, but the difference in vsync polarity willFHD Mod (PCB Rev. A1.04, FW Rev. <red>) EDID wrote: Section "Monitor"
...
DisplaySize 310 170
Gamma 2.20
Option "DPMS" "true"
Modeline "Mode 0" 138.65 1920 1968 2000 2080 1080 1083 1088 1111 +hsync +vsync
EndSection
surely prevent us from using the NV140FHM with the FHD Mod.
I wonder if changing the EEPROM on the FHD Mod would help here. The vsync polarity is a register value of the LVDS-eDP converter chip and its registers are probably programmed during startup. I have no idea if these values are fixed or taken from the EDID of the attached screen, read from the AUX channel. In the latter case an update of the EEPROM chip would be enough.
BTW, I don't recommend the NV140FHM as a panel, as the specifications of the AUO B140HAN01.x or the Chimei N140HCE-EN1 look better.
Cheers,
Joerg