Thrulines.
Can be pretty accurate, can be wildly in error, & everything in between.
I spent a fair amount of time going through the Thrulines and for a while I had linked into my tree over 130 DNA Matches, both via the Common Ancestor route and my the Hard Slog Method.
Once I had marked up a 5 generation Pedigree Chart with the predecessors who were the MRCA with each of my DNA Matches I could then see that I had DNA Matches linking to and via each of my Great Great Grandparents.
Then I set about creating Groups based on each of the 8 G GP’s, so 8 Groups as per the text below.
I then went through each of the DNA Matches who are in my Family Trees and assigned them to the appropriate Group.
As I was assigning each of them I also looked at the shared matches and assigned them to the same Group(s).
Next it was back to the tree and assigning an image of DNA Icon to each person in the branch from the DNA Match to the MRCA, this now allows me to easily follow the DNA pathways in my trees.
Now when I look through my DNA Matches I can see those who have not been placed into the trees, the Unknown have their own Icon and Group.
Since I originally created the text below I have added another Group, this one is labelled with a ? icon to signify Thrulines that do not compute.
A lot of work, yes, but now dealing with new DNA Matches who are of interest is an easy weekly task.
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DNA Grouping.
Firstly print out a 5 Generation Pedigree Chart.
For the 8 Great Grandparents label each of them on the Pedigree Chart with a number, starting at 1 and going down the chart adding 2, then 3 etc up to 8.  Hence each Great Grandparent is given their own unique number in the 1 to 8 range.
There is method in this seemingly madness approach.
In Ancestry DNA there is now the possibility of creating up to 64 DNA Groups and you can assign DNA Matches to applicable Groups.  You can then filter the Groups so that only those in a selected Group will be visible and this is the Batch of DNA Matches that are going to be the main focus of your research, at least until you have gone as far as possible.
In my case I have created Groups as follows but Do Note that the first character of the name is displayed inside the coloured marker and hence why I chose to use 1 through 8 for the GGP’s:-
1 = 1 GGP
2 = 2 GGP
3 = 3 GGP
4 = 4 GGP
5 = 5 GGP
6 = 6 GGP
7 = 7 GGP
8 = 8 GGP
U = Unknown, these are the mystery ones, the ones left over.
As you build DNA matches into your tree you can assign the appropriate Group marker(s) to each of them.
Initially I would suggest you look at the highest DNA Match and then work down them to say those that share 75cM.  Assign each DNA Match to the applicable GGP Group(s) and assign the Shared Matches, irrespective of the cM that they share with the DNA Match to the same Groups.
If you are short of DNA Matches move down to include DNA Matches who share 60 cM then down to 50 cM if necessary.  Again assign Shared Matches to the same Groups.
With the DNA Matches who have not been assigned to any of the numbered 1 to 8 Groups, assign each and their Shared Matches to the UNKNOWN Group.
As an example say the Maternal Grandfather of the Home person is not known, then there should be no DNA match showing as included in Groups 5 and 6.  These ungrouped DNA Matches will be the centre of research and all of them and their Shared DNA matches will be assigned to the UNKNOWN Group.
Filter to view the UNKNOWN Group and then work through them one by one.
Whilst this process may seem a long and arduous process it will provide a strong foundation to develop your Biological Family Tree not just in finding the unknowns but in expanding the Family Tree.