Update!

I wrote to AskArt.com (which bills itself as the "Artists' Bluebook") to give them information on Georges le Serrec de Kervily's date of death and attached a photo of the portrait to illustrate the story.  A "content manager" wrote back a few hours ago to let me know that based on the information I supplied, they updated de Kervily's page to list his date of death as "c. 1952" and requested by permission to post the photo of the portrait on the page.  How fun!  You can see Aunt Betty's portrait on the site if you click here.