I thought I had checked: ID is not (no longer) on the Sort list (connected or not) {I did see an odd one: has cover. This is NOT any of my available columns}
{id} is the number Calibre assigns when the book is first imported.
If you have peeked under the skirts, that is the ID.
book_title (##)
ID is also seen on the I(nfo) pane
Since it is assigned at initial import, you can sort on that, even if you tamper with {date}