That is a good question.  I have assumed that the comments are stored in the AC database somewhere.  
I previously asked about whether there was a way to print a log of these comments other than accessing them one at a time with each item.  No one replied, so maybe we don't know how it works.  Perhaps we have to ask the Angels. 
So, since I have been unsure where the comments are in the permanent record, I don't use the comments, but actually create a message for any important actions generated by review of an item.  That way, I have a record in the prior encounters.