I plucked my copy of the book from the shelves and have started to re-read it.

One thing in the introductory chapter (where the terms are defined, etc.) is that expedition after expedition, since the 1930s, have found zero Clovis-type points in the postulated ice-free corridor from Beringia through Alberta. Nor have Clovis-type points been found in Siberia.

People wander, people migrate (witness now!). With the maximum spread of ice and the resultant decrease in sea levels more than one way would have opened up. I see no problem with people coming to North America via several routes and methods. I would even suggest that it's likely.