Dan,
It's possible, although rare, that the stalled mailings continued to run in the background.
It should be practically impossible for this to happen with v1.85. I highly recommend upgrading as it has much more advanced queue protection.
I cannot recommend that you continue to email a file attachment of that size. It is a *huge* demand on the server... Is it not just a well to simply include a link to the file hosted on the web site?
Regards, DW