Your main problem is, instead of date you have 2 entries with year numbers (integers)

Number 1965 has same value as date 18.05.1905, and number 1985 has same value as 07.06.1905.

In Excel, a date is really the number of days from 10.01.1900 (or from 31.12.1899 -
depending how you calculate this number)!