The dinner plates that Jacquouille drops and smash on the floor totally shatter yet a complete plate is kicked by Jean-Pierre as he walks through the smashed plates.
At the end of the film (and at the beginning of Les Visiteurs 2), Godfrey turns his crossbow to the left not to kill his future stepfather. But the crossbow during the next shot, turned to the right.
The horse Godefroy is riding which they found in the pasture after arriving in the future has no saddle, yet in several shots of him riding the horse a saddle is clearly visible. No saddle is visible once Godefroy jumps off the horse in the church.
The bathroom basin that overflows and floods the house has a overflow hole to stop it doing just that. It is clearly visible in a close up shot of the basin.
We can see that Sergeant Gibon (which is actually staff sergeant) carries a badge of the Picardie region of his uniform shirt, in the second part of the police captain is wearing a badge of the Burgundy region. The ranks of the police are not respected; the captain is subordinate to the staff sergeant.
When Godefroy arrives at Béatrice's, he complains that "there's no longer any hectare of forest". Hectare is a surface area unit that was invented during the French Revolution.
The arms of the king of France visible on the trumpeters' trumpets welcoming his return to camp are three lilies: one in chief and two in base. At the time, the arms of France were semé-de-lis("sown with lilies"). When they are reduced to three, they will be two in the chief and one in the base.
(at around 1h 04 mins) When Godefroy is on the phone to Jaquard at the bowling alley, the microphone can be seen darting about just above the clock on the mantelpiece.