mailing_formats/ma_trans and bounce_stats show different number of bounces

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I was trying to report on the mailing deliverability of mailings so I checked out the two tables mentioned above. The bounce statistics table shows more total bounces (less than 1% more) compared to the mailing_formats and ma_trans table for most mailings. Does anyone have any idea why the bounces statistics table could be showing more bounces than the mailing_formats and ma_trans table? The difference is not coming from any one of the individual bounce types broken out in bounce_stats (Soft, Hard, Content, Sender, etc.), so it seems like multiple types are contributing to this difference. The Hard and Soft