> A minority of the problems in the exams were seen by the model during training

A minority can be 49%. They do mention they tested against newly available practice exams, but those are often based on older real exam questions which may have been discussed extensively in forums that were in the training data. Now that it is for-profit ClosedAI we have to somewhat treat each claim as if it were made adversarially, assuming minority may mean 49% when it would benefit them one way and .1% when it serves their look better for sales pitch to the Microsoft board, etc.