Christian of the eSheep was kind enough to write back. This makes me happy; I love it when people are willing to talk about how things work.
The privacy-concerned will be happy to know that scans have stopped until improved privacy tweaks are added. If you want your items removed, they're now removed almost immediately.
I'm not the only one who found the phrase "private islands" confusing. Currently any parcel (mainland or island) that Grid Shepard can enter gets scanned. The wording on the search has been changed to make what is and isn't scanned clearer. The parcel scanning pattern is a little strange - some of my items on one parcel are listed under the name of two others, but not under the name of the parcel they're in. Maybe that was the parcel Grid Shepard was in when doing the scan?
Only objects found in the last scan of the grid are listed. I'm not sure if the index is replaced or edited; based on what the search currently does, it makes sense to erase and replace. I think I'll ask about adding the day the last scan happened to the site.
Christian wrote that there's been a lot of work focused on making the results of the scans more complete. If the search only contains information from the last sweep, the results need to be a more accurate for the search to be a useful shopping tool. I have scanned prim-for-sale vendors which are rezzed side by side with ones that were not.
She (yes, Grid Shepard has a gender) is not using lsl, instead she's taking note of what she sees. It sounds like Grid Shepard is operating with an edited client. That has me wondering if the items missed were because of view occlusion or slow grid db response.