If the current BIOS version that you are running has a newer ME firmware than the one you are trying to downgrade to the firmware flash is not supported. Both of those versions you list are very early builds. Why would you want to go back that far?
from the documents:
Downgrading the BIOS to an earlier version is not recommended and might not be supported. An
earlier BIOS version might not offer support for the latest processors, bug fixes, critical
security updates, or support the latest board revisions currently being manufactured. If you are
trying to downgrade to a previous BIOS version and its Intel® ME Firmware version is older than
that currently on the
motherboard, then the downgrade is NOT supported.
You shall not downgrade your bios and specially not the very old version. For your information before bios version 0042 was released it was very common that NUC caused Windows crash (blue screen BSOD failure). After this failure happens only replacing NUC was fixing this problem. This was fixed only form bios 0042 ( Improved electrical over-stress protection in the voltage regulator circuitry).
In order to install Windows 7 on your NUC, you shall add USB3 driver to yours Windows 7 installation media. Use the Intel tool and instructions from Amy's post above.
Think also to install Windows 10 instead of Windows 7 and the installation shall go smoothly.
Adding to Leon's response, whomever was telling you that you needed to downgrade your BIOS didn't know what they were talking about and are leading you astray. You do not need to do this. I am regularly installing (and reinstalling) Windows 7 onto older (4th, 5th and 6th gen) NUCs and I always, always do so with the most recent BIOS installed. Really, the only trick necessary is to get the WIM files fully updated with the USB 3.0 drivers.
P.S. I would love to provide you with my installation image, but I don't have any place that I can upload a close to 4GB ISO file.