These are the only 20th century cardboard puzzles that I have actively tried to collect. Some observations from my incomplete set.
 
 | 1 | untitled (American Sailing Ship) | 
| 2 | Deauville Races 1932 | 
| 3 | Boat Race | 
| 4 | The Prairie Fire | 
| 5 | King Arthur's Country | 
| 6 | Little Birds of the Shore | 
| 7 | Sheridan's Charge | 
| 8 | Thanksgiving | 
| 9 | Buffalo Hunt | 
| 10 | The Jolly Flat Boatmen | 
| 11 | Green Sleeves Leads the Way | 
| 12 | Winter** | 
| 13 | Dogs | 
| 14 | Sunset | 
| 15 | Wild Horses | 
| 16 | Between two Fires | 
| 17 | Milady of the Tavern | 
| 18 | Charging Elephants | 
| 19 | Merchant Ship | 
| 20 | Washington at Mt. Vernon | 
| 21 | Pickett's Charge at Gettysburg | 
| 22 | Boyhood of Sir Walter Raleigh | 
| 23 | Hunters | 
| 24 | Important Question | 
| 25 | So Near Yet So Far | 
| 26 | The Defense | 
| 27 | A Quiet Battle | 
| 28 | Sunday Morning in Norway | 
| 29 | The Fortune Teller | 
| 30 | Acrobats | 
| 31 | Dance of the Minuet |