Hi Chris,
Please read my article in Edition 120 – Summer 2021 of the Dufour News. Take particular note of the advice on page 12. Past issues are available in the Member's section of this site.
If done properly these repairs are stronger than the original. However, you should not be seeing stress cracks which indicates to me the repairer did not grind back enough to good material, or too few laminations of cloth and matt were used, or maybe it has had a subsequent grounding now requiring it to be done again.
Establish the full circumstances of what happened and why it was repaired, repaired by whom, the extent and specification of the work done and get satisfactory openly given answers.
However, if no documentation is available (as you say) – personally I would walk away from it.
The membership association for owners of Dufour Yachts