In the last scene, Hogan reads a note from Nimrod that Carter found in the model plane set. In close-up, Hogan is holding the note in his right hand. When Hogan finishes reading the note and the shot widens for a reaction shot, Hogan is now holding the note in his left hand, and the model's plans in his right.
Just before Newkirk enters Klink's office to clean, Hochstetter is ready to give up and about to call for a cryptologist. In this shot, there's one thin layer of crumpled up yellow papers covering part of Klink's desk from Maj Hochstetter's attempts at deciphering the coded message. When Newkirk enters the office, the wrinkled yellow papers on the desk are suddenly piled very high and cover the whole desk.
When Klink is kidnapped, Karl hands Schultz a note (the ransom note). When Schultz shows the note as he tells Klink he's going to wait five minutes, it is much larger than the note he was handed - with no sign that the note had been unfolded to make it larger (i.e., there are no creases in the paper).
In the opening scene where Hogan is checking out the German compound, one can see several 1960s vintage cars in the compound.
Hogan takes a series of model boxes, supposedly of the Hindenburg. The one on the bottom is a 1960's era kit of a JU87 Stuka dive-bomber. Carter is later seen working with this kit.
It is unlikely a kit of a Stuka would be available in WWII.
The model kits that Hogan takes are kits from the late 1950's at the earliest. These kits would not be available during WW II.
After Klink tells Hogan that he has to pick up General Burkhalter, Hogan goes back to the guys washing Klink's car. The men all crowd around Hogan complaining about him, then Schultz leaves. Hogan then says, "Ho-o-o-ld it. Klink's gotta pick up Burkhalter at the station. This is one time we're gonna give him all the help we possibly can." It appears that a sound system malfunction occurred just before Hogan says 'it', as it is not audible. All that is audible is the 'Ho-o-o-l' part. The rest of the line is obviously dubbed in, because no background noise is audible, and the sound of Hogan's voice is slightly different.
There are several instances where a production light is reflecting in Klink's monocle.
The Underground agents would know the difference between a Colonel's uniform and a General's; however, they still mistake Klink for a General.