Sent emails during the period for 05/01/13 thru 10/06/14 did not show up in the sent box as and when it was sent although recipient received it. For example, I sent email right at this minute and right away check the sent box but it wasn’t there but recipient did received the mail. After 10/06/14, this problem was corrected by itself, meaning: the sent emails were registered in the sent box as and when emails were sent. What caused this problem and Is it because to recover these sent emails?

PS: My gut feeling is that during this period yahoo was doing some changes to their system or classic email and so may have had impact on the sent emails