I have an advantage, I have decades of experience based in training investigating cold cases.  Rarely is a single record going to solve a cold case. What solves a cold case is how one looks that the data they have available.  I am most familiar with researching the Irish but I am sure much can be used with any genealogy research so In 2010 I turned to science, I submitted a 37 marker Y-DNA test to Family Tree DNA and then upgraded it to 67 markers, then 111 markers and while my matches help me know that my family was not Hy-Many as all those books written about my family claim, the matches and records of my matches indicated that we were Clann Ceallaigh of County Fermanagh but I still didn't have proof.  That came later when I upgraded to Big Y 500 and then to Big Y 700 and as the Family Tree Data base grew new database tools became available.  Now 14 years later I have the proof I needed.  My Biy Y 700 matches to Pollnagollum 911 R-FGC11134 who lived about 4200 years ago and was found in the Pollnajollum Cave in Co Fermanagh and Treanmacmurtagh 116 R-FGC11134 who lived about 4000 years ago found in a cist burial inside a cairn in Co Sligo cements my Y DNA in the right places and the right time and combines with the records and family stories of my 111 marker matches that is proof that I am of the Clann Ceallaigh of Southern Co Fermanagh Ireland.