Can I renew my O-A Visa by leaving and re-entering Thailand just before it expires?

A yearly extension of stay that you get from the immigration office <- this is NOT a visa. There is also a re-entry permit on that page to allowing the holder to exit/re-enter the country and not have the extension canceled.

A year-long, multi-entry Non-Immigrant Type VISA <- that you get from a thai consulate in YOUR country before you wing your way here.

A VISA expires when it expires and a visa or an extension can NEVER been renewed

You could have gotten 2 years out of the O-A visa ONLY while the visa was still valid.

Now that you are on yearly extnesions of stays from the immigration office you CANNOT get another 'free year' by exiting re-entering.

You are confusing a VISA with a yearly extension of stay

you have not been here on ANY visa for the last 7 years. You've been on yearly extensions of stays that you got from the immigration office