Hello Majken,
The duplicate checking function will look through all items by default but there is a way to do what you are asking.
The duplicate checking function will ignore items that have been marked as 'Deleted' (assigned the 'D' flag). If you assign the 'D' flag to all of the items that you want ignored then the duplicate checking function will only look at the remaining items.
I had a look at your review and it appears that you do not have any items marked as 'Deleted' at this point. As well, it appears that you have already run the 'Get new duplicates' option but have yet to mark any items as duplicates.
What you could do is reset your duplicate checking. This is done in the 'Manual/Advanced' tab in the 'Manage duplicate groups' window. You want to run the second reset option which will delete all duplicate information. Once you have done that you would then assign the 'D' flag to all of the items that you want the duplicate checking functions to ignore.
You should now run the duplcate checking function again. It will ignore the 'D' items and only look at the items that are left. You should then run the Mark automatically' function and finally, sort out the remaining groups manually.
Once that is done you can change all of those 'D' items back to what they were previously.
I should mention that if you decide to run the duplicate checking later on (including the items that you had the system ignore previously) you will probably end up with a number of overlapping duplicate groups. There are functions in the software to deal with that scenario although it may take a bit of time to sort them out. To avoid the overlap scenario you can do a 'partial' reset of the duplcate checking before you run 'Get new duplicates' against the previously ignored items. This is the first reset option (in the 'Manual/Advanced' tab in the 'Manage duplicate groups' window). A partial reset will removed all existing duplicate groups but will still keep the duplicate checking information from before. Without the existing duplicate groups there will not be any overlapping groups to deal with.
Best regards,
Jeff