It's actually a List<Tuple<date, number, rowid>>> in sorted order, and queries are more akin to binary search (they are not actually binary but use a wider fanout depending on many factors)
Yeah it might be closer to what's actually happening but it doesn't make it obvious why something doesn't work. The map model doesn't even cover non-unique indices. Or different type of indexes.
It's _not_ just a list in sorted order; if it were, you could not insert efficiently into it. But the tuple is the right mental model, indeed.