What’s the difference between ‘as much, if not more, than’ and ‘as much, if not more, as’?

Both examples have odd syntax. Written in full, the first would be:

. . . he seemed determined that everyone should enjoy themselves as much as they would have done at Hogwarts, if not more than they would have done at Hogwarts . . .

To express the same thing elliptically it is necessary to write:

. . . he seemed determined that everyone should enjoy themselves as much as, if not more, than they would have done at Hogwarts . . .

Applying the same process to the second example, we get:

The imports in 1877 amounted to as much as those in 1876, if not more than those in 1876.

Elliptically:

The imports in 1877 amounted to as much as, if not more than, those in 1876