Think I might have an error somewhere. If not everywhere.

I think you might find it easier to set up a table which logs progress for each execution and then use that to drive subsequent executions.

Would require some...

Select Column1, VirtualColumn = iif(Column1 = 'N1', 'Antony', NULL)
From Table

Using SQL Server to check for file existence from within an SSIS package seems inelegant.
Have you considered creating a script task to do this?
It's very easy in C#...