Which wouldn't matter if CW had a backup, and if that were possible she'd treat it as a survival priority. The implication is that AI personalities can't be backed up, despite the early comic that showed Pintsize running on a desktop.
There are a few possible explanations:
1. This relates to Gyrre's point. Perhaps the less-advanced pre-Singularity AIs didn't have a physical brain and were thus able to transfer their consciousnesses freely.
2. CW and the other underground AIs also might have been able to make a backup but not created one for security reasons, which would explain the extra emphasis on drive safety. This implies that full consciousness transfer is possible, so maybe every chassis made has an unused AI brain inside that molds to match the mind of the AI trying to transfer into it. Secondary thought: this process is painful and feels self-intrusive, similar to Yay going inside someone's mind and editing it.
4. AIs can temporarily add a copy of their consciousness to the computer, but cannot do the machine learning process and cannot make complex decisions.
5. The tech has changed over the years and the earlier AIs (Momo, Winslow, Pintsize) have received hardware and/or firmware and/or software upgrades in order to keep up.
Or, we could all be missing the most likely reason, which is that Jeph forgot about a minor detail put in the comic fifteen years ago.