Greetings,
You may run "Media Set" report in Backup Exec 9.1 which will give you a list of tapes with modified date and allocation date.
The "Media Set" report lists all media sets and media used by Backup Exec servers. Usage statistics are given for each piece of media.
However, there is no specific report that only has "Modified Date" and "Allocation Date".
Hope, this answers your query. If you have further queries, please let us know.