How to verify an ADB backup file is complete and in a good state?

This is not a duplicate of How to verify a backup file from ADB backup. The poster there probably didn't know that an unrooted phone requires -nosystem (ref) and ended with a 0 byte file, where my backup file is almost 8GB.

Given that adb gives almost zero feedback on it's backup progress and success or failure. How can I be confident that the backup I've just completed is a good one? and that it contains what I think it does? and that it will (probably) work to restore or extract data from?

I have the one android device (Nexus 5), access to Win7 PCs, and ubuntu virtual machines if needed.