How does Squealer explain the conflict regarding the wording on the cart?

Squealer claims to have been present at Boxer’s death, a tale he relates emotionally to the other animals. He claims that Boxer’s last words were, “Forward, Comrades! … Forward in the name of the Rebellion” and “Long live Animal Farm! Long live Comrade Napoleon! Napoleon is always right” (125). Squealer also claims that the van belongs to the veterinarian, who had recently bought it from the horse slaughterer and had not yet managed to paint over the lettering.