Absolutely..... evidence of sponsor oversight should be maintained in the trial master file. Where study responsibilities are outsourced, part of the TMF may be established and maintained by the CRO (and possibly in a different system to the sponsor's documents) but the sponsor still has a responsibility to maintain a TMF for those documents that they are responsible for. I really do not like the term "Sponsor Oversight File" because it gives the impression that this is not part of the TMF (similar actually to the 'Investigator Site File'.... which is also part of the TMF!).

The TMF Reference Model provides some guidance regarding what type of documentation may be kept by the sponsor as evidence of oversight. However, each sponsor needs to make this determination for itself at the start of the study. There needs to be an oversight plan and so this plan will identify what documentary evidence should be created and maintained (per MHRA GCP Guide).