Be aware that when there are two operators for the same fingerprint, a situation could arise where we need to add points before the end of the series and cannot simply append. E.g. two interval ops with these interval points spaced like this:

```
|   |   |   |
  |   |   |   |
```

I think it's not actually possible for a user to construct a query resulting in two ops like that, though (but that is a higher-layer thing).