Is there a way to view historical session data for a project that has exceeded its error allocation? If so, how can I access this information?

Yes, but this historical session data is categorized only per release. You can view it in your Releases Page by choosing a specific release. If you expand the graph options, you can see information such as the crash free session rate, the session count, etc. between all releases and your chosen release.

You can also build custom dashboards that will show you session data.