Fossil allows mistakes to be corrected (for example, check-in comments can be revised, and check-ins can be moved onto new branches even after the check-in has occurred) but the correction is an addition to the repository and the original actions are preserved and displayed alongside the corrections, thus preserving an historically accurate audit trail. This is analogous to an accounting practice of marking through an incorrect entry in a ledger and writing a correction beside it.
The lack of a "rebase" command and the inability to rewrite history is considered a feature of Fossil, not an omission or bug.