The Bobbie's defining trick is that it puts a full holiday plate, including the stuffing, inside a sub roll, which means it is bread wrapped around more bread. A Thanksgiving dinner is roast turkey, cranberry sauce, stuffing, and gravy or mayonnaise eaten with a fork. The Bobbie compresses that into a long roll and asks it to be held in one hand, and the whole engineering problem is keeping a wet, soft, carbohydrate-heavy filling from turning the roll into paste. It succeeds by treating the stuffing as a structural layer rather than a scoop of side dish, and by using the roll's crust as the only firm element in an otherwise uniformly soft sandwich.
The craft is in moisture control and the build order. The turkey is pulled or sliced and used in enough volume to be the spine of the sandwich rather than a thin layer lost under everything else. The stuffing is packed in as a dense, herbed layer that absorbs and holds moisture instead of shedding it, which is what keeps the cranberry from soaking straight through to the bread. Cranberry sauce supplies the one sharp, acidic, faintly sweet note that cuts an otherwise rich and savory build, and it is placed against the meat rather than the crumb so its juice does not run into the roll. Mayonnaise goes on the bread as a fat seal and a stand-in for gravy, since real gravy would collapse the whole thing in minutes. The sub roll has to have a tender interior and a crust with enough structure to carry a heavy, soft, slightly wet load the length of it without folding, which is the same demand every long-roll sandwich makes, here under unusual pressure.
The variations are mostly seasonal and additive rather than structural. A version with gravy added pushes it toward the hot plate it descends from; a hot, griddled reading warms the turkey and stuffing and loosens the cold-sub balance; some builds add a sharp cheese against the cranberry. Each of those is a codified change with its own logic and deserves its own article rather than being crowded in here.