Birthdays - but which one?

One of the slightly unusual features of the Scottish system of statutory registration is the Register of Corrected Entries (now known as the Register of Corrections, Etc, or RCE). This allows for errors in original records to be corrected. In modern times, the RCE is a separate volume - the original register is not actually changed; instead a note is added in the margin, with a reference to the RCE.

​While the RCE system only applies to statutory registration of births, marriages and deaths, as introduced in Scotland in 1855, it was clearly not without precedent, as the following entry from the Kirk Session of Barony, in Glasgow, shows:

31 October 1832
Compeared Mr John Hamilton who stated to the Session that he had lately discovered that a mistake had been made in the Register of Births belonging to the Parish which related to the recording the date of the birth of his lawful twin children a daughter & son named Mary Ann & John, and which he requested that the Session would have the goodness to get rectified. The mistake was this, that it was recorded, that these children were born on the 10th & 12th of November 1811 years whereas the truth is, that they were born on the 10th and 12th of October 1811. The Session satisfied of the truth of the above statement unanimously agree to Mr Hamilton's request, and do hereby order their Clerk to insert anew the birth of his twin children named Mary Ann & John born on the 10th and 12th October 1811 years, into the Parish Register of Births and Baptisms.
[Glasgow Barony Kirk Session CH2/173/13 p. 89]

Several things stand out from this entry. Firstly, it shows that even contemporary, primary sources can be incorrect: although in this case, it seems that the clerk did change the original register, and a modern researcher would find the correct date (assuming the father was telling the truth). Secondly, you have to wonder how and why the father noticed the error, almost exactly 21 years after the event. Perhaps the children were involved in some legal matter that required them to be 21 years of age, possibly an inheritance. And thirdly, it also inadvertently offers a glimpse into family history as opposed to genealogy: Mary Ann and John were twins, but they were born 2 days apart, suggesting that their mother (unnamed in this entry, but she was Agnes Robertson) must have experienced a lengthy labour of at least 24 hours, more than 35 years before James Young Simpson pioneered the use of anaesthesia in childbirth.