I'd set all my jobs to Overwrite and not worry about Append periods.
If you just need the dailies for a week, (that is, when this week's monday runs, you don't care about last week's monday data any more), then I'd set the OPP to 6 days( just in case the backup runs past midnight)
Also be sure from tools\media management that overwrite protection is either full or partial and that you have selected "Use overwritable media in the target media set before scratch media" But that still won't avoid the problems of having two sets of BKF files with the same name, but different creation dates and data.
If you could use BackupExec to do the D2T backups, you could just do a Duplicate Job, and the catalog would retain the info for data on the tapes, and you could restore directly from tape, rather than having to restore to disk, inventory, catalog, restore
.Sounds like you are in a No-Win situation to me