Ways to get around pre-registration?
The value of preregistration for a retrospective study is pretty marginal. Preregistration works best for prospective studies where the primary analyses and hypotheses to be tested are finalized before data collection begins. It is worth noting that preregistration does not prevent data fabrication or many other types of scientific misconduct. The main benefit of preregistration, beyond making the process more open, is by preventing p-hacking and HARKing. This only works for new data, or at least for new aggregations of existing data.

The worse abuse of preregistration I have seen is a study where the hypothesis and planned analyses where changed 6 months after data collection was completed. The paper then talked about the planned comparisons from the updated version of the preregistered study.