Hi Hannah,
You are correct that this data is not exported when you export from the Project. This only exports the Work Plan. As for your questions regarding backup...
We do backup the data. Here is a breakdown of how...
For all customers, we do daily backups that run at night (PST). The back is incremental but ultimately you could be looking at losing up to 1 day of data entry. The number of daily backups is very high and in fact goes up to one year but the older the backup the more risk. The process is complicated and needs to be restored to a staging environment. Then any subsequent updates/hotfixes need to be applied and stability/information needs to be confirmed.
Notes:
It is easier to restore an entire customer instance rather than one object (i.e. Discussion or Project). Restoring specific objects entail further risk that can cause corruption, failed restores and odd behavior after restore.