Fascinating, and well done for all the work. Some of them are not the flag of a country though, to be clear, just "a flag that someone found" (eg. Benin, Iran), while the Russian and Turkmen ones are a mystery - they've never been the national flag, at any rate. Thanks, though.
Thanks for the feedback, generally I tried to base my flags based on the oldest polity that was "centered" in the modern-day country (as in capital located there or founded there) which had a flag. So for Russia and Turkmenistan, the flags I took were from Muscovy and the Ghaznavids, respectively. For Iran, the flag is a depiction of the Shahdad standard, an ancient metallic standard found in Iran. It is doubtful it was ever a national flag but I included it because it holds the title of one of the oldest known flags in human history. I guess part of it comes down to what is considered to be a flag representing a particularly country vs just a flag that represents a group that happens to be located in that country, and I was more liberal with that definition to find flags as old as possible.