This might require someone from NVIDIA commenting, but basically what I see is a valid EDID, and your earlier mentioned 720x576 is an extension mode. The natively supported mode 640x480@60Hz is probably supported, but extension modes are not supported. If a mode is somehow set to a valid mode, and then a monitor is disconnected while a new monitor is then connected, it is possible the mode can end up working…but it would be luck where a native mode of a previous monitor happens to equal an extension mode of another monitor (the mode might be supported, but the setting of that mode must not be via an extension…one monitor with a native mode can be used to set a mode which is the extension to another monitor).
Similarly there may be some default mode which happens to work with a monitor and that monitor uses that mode via extension…this would simply work, but it wouldn’t be due to EDID succeeding.
Do you have another more “standard” monitor you can check to see how it works?
Note what was said earlier by @Honey_Patouceul, about “
ModeDebug” in the X config file. If this is in place, then once you’ve booted with a given monitor attached the Xorg log file will verbosely tell you what it thinks about every single mode reported by the monitor. This could confirm accept/reject of particular modes, and the driver itself would tell you why the mode is rejected for reject cases.