This one has come up a couple of times, so I'll address it. First, sorry if I didn't spell everything out in explicit detail. With that said, it is a matter of interpration based on context. In the context of the scenario, the restore is starting with the Monday night full backup, what is the latest differential backup? Answer, not the one taken at 8:00 AM Wednesday.

If I tell my co-worker I am restoring the Monday night full backup, tell me what the lastest differential backup is while I get this started. I would expect him (or her) to look up the correct file with my having to specify "based on the Mondays Full Backup."

Now, if this individual is a new junior DBA, and wasn't sure, I'd expect them to ask. I'd also be making sure that they learn about backup/restores as they may find themselves having to do it when I'm not available to assist.