There are many cases where the law has filled the gap in a case by presuming an action or document exits going back to the “limit of legal memory”. The date of this is 3rd September 1189 as set by the Statute of Westminster 1275.
It is interesting to speculate on why this date was chosen. 3rd September incidentally is a date with “a history” in British history. It was the date of the battle of Dunbar in 1650, date of the battle of Worcester in 1651 (two of Cromwell’s greatest victories), although it was also the date he died in 1658.
So why should 3rd September 1189 be the date considered by lawyers as the beginning of time immemorial or the limit of legal memory, so important as a limitation period in real property? Pollock and Maitland offer this explanation:
‘Probably this date (1189) was then chosen because it was just possible that a living man should have been told by his father of what that father had seen in 1189, and in a proprietary action for land, the defendant’s champion was allowed to speak of what his father had seen.’
The restless Henry II had gone to his grave; his reforms were beginning to take effect; our first classical text-book had just been written (Glanvil 187) the strong central court was doing justice term after term on a large scale; it was beginning to have a legal memory which would ensure for all ages in the form of a magnificent series of judicial records. Our extant plea rolls go back to 1194, the greatest series of the ‘feet of fines’ (or final concords or compromises between litigants) begins in 1195.
We shall never know definitively, however for proof of ownership to Lordship rights (the Seigniory) it is still one of the most important pieces of law that is in force.
 Michael L. Nash: 1189 and the limit of legal memory, 139 New Law Journal 1763