From Part M AMC M.A.305 (h) "...Reconstruction of lost or destroyed records can be done by reference to other records which reflect the time in service, research of records maintained by repair facilities and reference to records maintained by individual mechanics etc. When these things have been done and the record is still incomplete, the owner/operator may make a statement in the new record describing the loss and establishing the time in service based on the research and the best estimate of time in service. The reconstructed records should be submitted to the competent authority for acceptance.
NOTE: Additional maintenance may be required."
Note that Part 145 does not require the AMO to send maintenance records to the owner/operator; merely details of mods, repairs, CRS and the LBE. The 145 org only has to retain records of maintenance accomplished by them for 2 years from the date of that maintenance.