Upvote:10
You recorded your parent's birth date incorrectly in a previous application and discovered the error in preparing a T2 application. They know that people make clerical errors and they will be reasonable about if several hurdles are cleared...
I assume most of your answers are 'no' or 'not applicable'. Lots of stuff we see here are cases where items 1 and 2 fail and that leads to more difficulty in clearing items 3 and 4.
Some applicants do not know who their parents are and lots more of them don't know their birth dates. As long as your parent is not notorious in some way that would affect item 4, I would offer something along the lines of...
In completing this application I had access to more authoritative materials than when I applied in 2014. Accordingly, my father's birth date has been recorded correctly in this application.
or...
Because of its importance I had this application double-checked against source and this resulted in a correction to my father's birth date. The correct value has been recorded on this form.
...or any other similar statement. Note that these statements are free from apologies or lengthy digressions, and above all they do not tell the ECO what to think (they do not like that).
Note: Sometimes a question will come up asking if an applicant should persist an error made in an earlier application. Their rationale is that it's more convenient if everything sync's up. But the answer is emphatically no, never persist a previous error. It fails on item 3.