Some systems never heard of Y2K.
Many programs in operation today, terrible programs written by lazy developers, still represent four-digit years with only the final two digits, making the year 2000 indistinguishable from 1900.
If you’re consuming data from a source system using an incomplete date format, and you’re doing your job properly, you’ll want to correct for that.
Below is an ADF expression example that will correct date field values that relate to the year 2000 onward by prefixing 20 to the year, e.g. 21 becomes 2021.