In "The Necklace," how does the jeweler scene foreshadow the end?

After Mathilde Loisel wears Madame Forestier's imitation diamond necklace all night during the ball, she discovers that she has lost the necklace when she arrives home. Unfortunately, her husband cannot locate the missing necklace when he retraces their steps. After a week of searching for the necklace, Mathilde Loisel visits the jeweler whose name was on the jewelry box that once held Madame Forestier's necklace. The jeweler proceeds to consult his books and tells Madame Loisel that he never sold the necklace to Madame Forestier and must have simply furnished the case. The fact that the jeweler had never sold such an expensive necklace to Madame Forestier foreshadows Mathilde's discovery that the necklace she lost was an imitation. Mathilde proceeds to purchase a genuine necklace that is similar to the one Madame Forestier let her borrow for thirty-six thousand francs and works tirelessly for ten years to pay it off.

The day after Madame Loisel loses what she thinks is a highly valuable necklace, she goes to the jeweler whose name is inside the necklace's empty case. She hopes that the jeweler can help her find an exact replacement for the missing necklace before Madame Forestier finds out. Unfortunately, the jeweler is not much help. He closely consults his sales records and finds that he hasn't recently sold any such item matching the necklace's description; he must have only supplied the case. This is ominous news indeed, but Madame Loisel is either too slow to draw the necessary conclusions or perhaps just so desperate to track down a replacement that she doesn't catch on.
At any rate, the episode at the jeweler's foreshadows Madame Loisel's subsequent discovery, many years later, that the lost necklace wasn't really a valuable piece of jewelry at all, but a fake. If it really had been such a precious item it would have been supplied along with the case.