That is my understanding as well. A shame - If they survived this long and without or coping with the insect so far why not allow historical ungrafted sites an exception at the very least.
I wonder if layering counts, I mean if a branch happened to end up in the soil reaching out to the spot of a removed old/dead vine…
Layering would certainly be a way to finesse the rule.
Tom
I believe that all of Calera estate vineyards on Mount Harlan are ungrafted.
no, just Mills. Possibly some of the white blocks too.
Yes, I think some of the Calera Viognier and some or all of the Chardonnay are also own rooted.
-Al
Those are fairly isolated from other vineyards, right?
Yes. Calera is the only commercial winery in the AVA. Years ago Calera restricted visitors because of the fear of bringing phylloxera to the vineyards. This has since changed when they opened a tasting room on the property. This had led me to believe all the vineyards were ungrafted but I believe Keith and Al more than my own memory. 
That’s probably because the '80s-'90s phylloxera crisis in California actually affected grafted vineyards. There was a popular rootstock in use which turned out not to be phylloxera-resistant. Ooops!