Files moved to trash- permanently delete?

How to remove/delete files with C1?
This is a multi-part inquiry.
In a previous post I asked for assistance with preview icons that had "?" in them. The given reason was due to the deletion of these files outside of C1. The instruction given to avoid this was to delete the files from within C1 through the folder within C1's Library.
The option to "Move to Trash" is chosen and the files are placed in C1's "Trash" folder. From here I chose "Empty Trash". Selecting either "All Images" or the "Album" under Session Albums these icons still appear and w/ a "?" within a circle.

My question is: how do we effectively/efficiently delete files from within C1? This seems quite cumbersome... but it probably is my misunderstanding. I would greatly appreciate a thorough explanation of how to use delete/remove files without to much hassle.

Thanks,

Doug