Don't confuse build date with first registration date.
Does your car have the ID plate fixed to the firewall behind the clutch master cylinder? If so it's a MK 1 or 1.5. There is no way of establishing an exact build date prior to the end of 69 when ADR plates were introduced.
The later type wiper panel was introduced in early/mid 68 and was used on late Mini Deluxe and MK1 Cooper 'S' cars, the so called Mk1.5 cars, Like mine, and continued through to the end of production in 78.
The interior trim is identical on Mini Deluxe and MK1 Cooper 'S' cars (apart from floor covering) and there are 2 types. The 2nd type was introduced at the same time as the wiper panel change. The first type was the same as 997/998 Cooper cars and was used in the Mini Deluxe and Cooper 'S' cars prior to early/mid 68.
Mini K and MK2 Cooper 'S' cars use the same trim but it is different to the 2nd type Mini Deluxe- MK1 'S' trim in both style and material.
I don't believe there were any MK 1 Cooper 'S' cars built in 69 as you couldn't buy one in your preferred colour until May when the MK 2 went on sale. Any MK 1 cars bought in early 69 would have been built in 68 and you had to take whatever colour was in stock at the time. I bought mine in Jan 69 and the colour choice was very limited.
Don't know if it helps but that's what I remember from 69. Others may disagree.
Regards
RonR