With the help of one of my American cousins we think we have found the solution to this.
Where there is the designation 'Senior' against a name (sen), Ancestry's search engine is showing the name as Esquire MD. No idea why but it's obviously a glitch in their program.
We have tried with many name searches over several counties and it seems to be the solution which would account for over fifteen thousand entries returning this title.
No point in telling Ancestry this as they don't listen.
So I'm posting it here in the hope it will be of help to others who encounter this glitch.