Puzzle #111731267 - 19 Crossed Pairs

Question

Instructions:
There are 19 pairs of related answers with a common theme. Each pair consists of an across answer and a down answer. These two answers cross at a single letter marked with a number.
All 19 pairs are related in a similar way.
Each numbered clue is for one of the crossed answers, either across or down. You will need to determine the other answer.
The final answer to the puzzle is 19 letters long.

1. Big name in U.S. sports equipment
2. LOTR film director
3. King of England in 1603
4. Dunder Mifflin salesman
5. Swiss folk hero
6. First U.S. postmaster general
7. Curious monkey
8. Fictional king of England
9. Small city in Kentucky
10. Portwenn doctor
11. Doubting disciple

… etc.

16. U.S. vacuum brand
17. Big U.S. auto maker
18. McDonald’s clown
19. Singer Swift

Answer 1

Firstly, let's find one answer to each given clue

1. WILSON
2. JACKSON
3. JAMES
4. DWIGHT (Schrute)
5. WILLIAM (Tell)
6. BENJAMIN (Franklin)
7. GEORGE
8. ARTHUR
9. LYNDON
10. MARTIN
11. THOMAS
16. HOOVER
17. FORD
18. RONALD
19. TAYLOR

Now notice that

Each of these answers is either the first or last name of a former U.S. president and the other name gives the other answer for the same clue. In particular, for the above the two answers are

1. WOODROW WILSON
2. ANDREW JACKSON
3. JAMES MADISON
4. DWIGHT EISENHOWER
5. WILLIAM MCKINLEY
6. BENJAMIN HARRISON
7. GEORGE WASHINGTON
8. CHESTER ARTHUR
9. LYNDON JOHNSON
10. MARTIN VANBUREN
11. THOMAS JEFFERSON
16. HERBERT HOOVER
17. GERALD FORD
18. RONALD REAGAN
19. ZACHARY TAYLOR

We can then deduce the unclued answers using the grid

12. BARACK OBAMA
13. MILLARD FILLMORE
14. WARREN HARDING
15. THEODORE ROOSEVELT

To complete the grid like this

The 19 highlighted letters spell out

WASHINGTONS BIRTHDAY

which is

22nd February 1732

However this is also

A holiday also known as Presidents' Day and is celebrated this year on 20 February, 2023 (today, at the time of posting).