In this case, 'several' is part of a larger grammatical context: 'the several States'. It's likely that modern interpretation extends the intent to the obvious

In this case, 'several' is part of a larger grammatical context: 'the several States'. It's likely that modern interpretation extends the intent to the obvious meaning 'the collection of States (that are part of the country)'. More modern math and logic terms might not have been in wide use at the time, and a 'group' of states sounds inherently ill defined. 'The States of the United States' just sounds silly.