I found these entries in NVTS.INF within the [nv_ClearRegistrySwitches]
section:

HKR,, Disable19x12x32at60
HKR,, Disable16x12x32ge70
HKR,, Disable19x10x32ge70

Could one of them be impeding the selection of the resolution I
require?

Within the same file, I also found this entry in the
[nv_SoftwareDeviceSettings] section:

HKR,, NV_Modes, %REG_MULTI_SZ%, "{*}S 640x400=39;320x200 320x240
400x300 512x384=9;SHV 1920x1440x8,16=19;640x480 720x480 720x576 800x600
1024x768 1280x800 1280x1024 1400x1050 1440x900 1600x1200 1680x1050
1920x1200=39;1920x1440x32 2048x1536=9;"

Again, the resolution 1920x1200 does show up in the list, suggesting
that it is in fact supported, even though it isn't showing up. Any
ideas?

Thanks