Do remember that Civil Registration of BMD’s commenced in Scotland on 1st Jan 1855 so quite a bit later than England and Wales.
Additionally to the advice given so far is being diligent in your tree with BMD inclusions, baptisms, census records as a minimum for each person with each record having multiple citations if possible.
I went back to 1841 with all my direct ancestors, obtained certs where there was doubt and one for my Great Grandmother confirmed she was illegitimate and hence I have the huge black hole in my tree.
Once I was confident my tree was correct I then expanded it sideways, generation by generation. Even then years later I found out my Paternal Grandmother had two Brothers we never knew about, we had seen them on the census records but never with their parents and it was only later in filling in the blanks mode that they came to life via an Ancestry search with only the family name, mothers maiden name and a search period of marriage year plus 10 with a tolerance of +/- 10 and the Registration Town or County, I use this technique a lot on the DNA matches to work out who those shown as Private in the matches tree really are.
Now the hard part, for each of the sideways family members I work out their BMD records as normal then add as much info as I can.
Having quite an extensive sideways Family Tree at Grandparent, Great Grandparent and Great Great Grandparent really helps in the DMA matching quest.
Alas Certificates do not always tell the truth, hence just because someone is registered as being the parent does not necessarily mean they are, there was a lot of stigma involved and hence anomalies come to the surface which with the advancement of science these now come to light and confuse the heck out of us.
Today I was doing my usual DNA trawl and clicked on a 80 cM match, then clicked on Shared Matches and at the bottom of the list was a 14cM with a tree of 1200 people so I clicked on them and looked at their tree and going back four generations a surname that I recognised from my sideways tree so had a branch mapped out to them very quickly. The odd thing is we both had the same Common Ancestors, word for word, identical spelling, correct dates and locations yet Ancestry never showed this DNA match as having a Common Ancestor with me. Hence Ancestry makes mistakes and has bugs as you are aware from my Bug thread.
What I have been doing today is to use the Note feature to add the Common Ancestors names to a DNA match who is now in a branch of my tree or I add the County where I believe the Matches and my Common Ancestor originates from, I use the Shared Matches to help deduce what to include. Doing this whenever I am viewing a Colour Coded Group then the line of their data includes the Note text which makes it easy to compare to the others in the Group.
I have 41 DNA Matches now in my tree and of them 27 are Cheshire based, 11 are Yorkshire and 3 North Lancashire, sadly my Welsh connection yields zero DNA Matches so far.
Stick with it and when the grey matter hurts, park the problem and move on, returning to it with fresh eyes.
My own anomaly, my 364cM Maureen “Lewis” match has been parked since last weekend.
