The Sandwich Tradition is defined by its bread, and specifically by a legal definition of bread. The baguette de tradition française is a regulated category: it may contain only wheat flour, water, salt, and leavening, with no additives of any kind and no freezing of the dough at any stage. A loaf made to that standard bakes differently from an ordinary baguette. It develops a darker, more blistered crust, an irregular open crumb with large uneven holes, and a flavor with more depth from a longer, slower fermentation. The Sandwich Tradition is any of the standard fillings built specifically on that loaf, and the bread is the entire reason it carries a different name.
The logic is that a better crust changes how a familiar filling reads. The tradition baguette shatters at the first bite rather than tearing, and its open crumb gives a spread or a layered filling somewhere to settle instead of compressing into a dense band. The longer-fermented bread carries a faint tang and a nuttiness of its own, so the ham, the cheese, or the pâté no longer has to compensate for a bland loaf; the bread becomes the most interesting element instead of the most neutral one. The filling itself is not the point and is often whatever the counter already makes well: butter and jambon de Paris, a young Comté, a country pâté with a cornichon. What changes is the surface underneath it.
The craft consideration is timing, which the tradition loaf makes stricter rather than looser. Because it contains no additives to extend its life, it stales fast, going from perfect to past it within a few hours of leaving the oven. A boulangerie that bakes in batches through the day can serve this sandwich at its best; one that bakes once cannot. The bread has to be filled while it is still close to the oven, and the sandwich eaten soon after, not held in a case until afternoon.
Variations are mostly a question of which filling the better bread is asked to carry, the ham-and-butter version of which is treated on its own as the Jambon-Beurre Tradition. A dry-cured ham, a slice of young cheese, a spread of rillettes: each is the same move, a standard sandwich built on a loaf held to the artisanal standard, with the bread doing more of the work than usual. It belongs with the place-and-context-keyed builds the catalog groups under Regional Specialty Sandwiches, and its specific contribution is the bread as the defining choice: a sandwich named not for its filling but for the regulated loaf it sits on.