1. You check the system views, whether the column exists on the table, if yes -- OK.

2. If the column does not exists you check for it in your mapping table, like this:

set @NewColumn = NULL

select @NewColumn = ParsedTableColumnName from mapping table where DestTableColumnName = 'your value'

3. if @NewColumn is not NULL then you have your parsed value, if not you can't do the update on this column.

You can insert this unparsed column in your mapping table with ParsedTableColumnName = NULL and update these rows manually, setting a value for ParsedTableColumnName.