In the past, imported brass locomotives and cars were packed and sold requiring some assembly to complete.
It was done that way to avoid the high US tariff that would be on completed models because for import duty they were classified as toys. Cheap imported toys were negatively impacting US toy manufacturers at the time
Anything requiring some assembly by a purchaser was classified differently at a lower tariff rate. For early imported locos and cars that usually meant once it was put together it could no longer fit into its box. That was a measure to assure it was not a finished model when inspected by the U S Customs Service.
S. Islander