Excel | nested IF statements using dates

I'm trying to calculate the number of months in a given time range that fall within 2019.

My data looks like this:

I changed the format of my Start Date and End Date columns to "date". The "Duration in months" and output column have number formatting.

I approached it as follows:

1. If Start Date (year) < 2019 AND End date (year) = 2019, take the number of months between 1-1-2019 and the end date.
2. If start Date (year) < 2019 AND End date (year) > 2019, the number of months in 2019 = 12
3. If start Date (year) = 2019 AND End date (year) = 2019, take the number of months between Start Date and End date.
4. If start Date (year) = 2019 AND End date (year) > 2019, take the number of months between Start Date and 1-1-2020.
5. For all other cases, the number of months = 0.

I then followed the instructions from this website for nested IF functions.

I came up with the following formula:

=IF(AND(YEAR(A3)<2019;YEAR(C3)=2019);DATEDIF(DATE(2019;1;1);C3;"m");IF(AND(YEAR(A3)<2019;YEAR(C3)>2019);12;IF(AND(YEAR(A3)=2019;YEAR(C3)=2019);DATEDIF(A3;C3;"m");IF(AND(YEAR(A3)=2019;YEAR(C3)>2019); DATEDIF(A3;DATE(2019;1;1);m);0))))

For the first 4 rows, it correctly returns 12. For row 7 and 8, however, it returns #NAME? .

No matter what I try, I can't seem to get it to work. Any ideas on how I can solve this?

Much appreciated!

Amy