How to determine compute module model over rpiBoot

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I need to flash an OS + some goodies to a RPI module. Currently I am using rpiBoot for this, following these steps:

start rpiboot - waiting for bcm...
plug in rpi over usb connection
mount the disk
configure/validate some partitioning
write the software to pi
validate
complete

Up until recently I have only worked with CM3 modules, so there's no need to double-check the compute module type. However, I want to be certain of the device hardware during this process - preferably right after mounting the disk. How can I do this?

I have been doing some experiments myself, but all information online points to using feature that are not available without the raspberry actually running such as:

cat /sys/firmware/devicetree/base/model

cat /proc/cpuinfo

I tried looking around in the /boot folder, but it seems to contain bcm... files for multiple versions, so that doesn't suggest an obvious solution.

How can I tell if the device that was mounted is a CM3, CM4, CM4S ( or CM5 in the future )?