It should not make any difference whether the records are adjacent in the sort order or not. Two issues might affect your results, It looks like you have dealt with one by using Show All Records. (Many users fail to set up their target fields with a found set of all records.) But make sure that you are importing your records into T05_Contacts and not some other occurrence of the contacts table. The other is in how you set up the field matching and whether the values in the fields are truly identical. (The addition of an extra space character, for example, is all that it takes to keep the values from matching even though it looks like they should match.) So it looks like your next step is to review what field matching has been set up in the import records step and then to double check the actual email address values for the presence of non-visible characters preventing a match to the data.
The third possibility is that you have encountered a new bug. If you can't find a reason for the records not to match by email address (as a test you might try setting up a self join on your T5_Contacts table to another occurrence of the same table--matching by email address to see if the imported data matches...) Possible bugs should be reported in Report an Issue.