Audit Trail can 'infer' who made a change on fields historically not available by Blackbaud. It does this by looking at the activities of users who have made changes to fields that are 'Changed By' trackable first and then 'inferring' that it is the same user who made changes to these non-trackable fields afterwards (within 10 minutes of the first changes taking place).
Depending on what field has been updated in Raiser's Edge and sent to Audit Trail first (as determined automatically by Blackbaud), Audit Trail can make these 'inferred' suggestions. However, Blackbaud sends these updates to Audit Trail in 1 minute batches, in no prescribed order and without an exact, to-the-second note of the time the changes made. As a result, when multiple changes made within the same minute (for example, when importing using Importacular) have occurred, Audit Trail will not be able to determine if a Changed By trackable field was changed first, and as such can not make any 'inferred' suggestions.