[Spoilers Extended] Can the series fit into two more books?

I don't think so. Here's why.

The first threat grows from the enmity between the great houses of Lannister and Stark as it plays out in a cycle of plot, counterplot, ambition, murder, and revenge, with the iron throne of the Seven Kingdoms as the ultimate prize. This will form the backbone of the first volume of the trilogy, A Game of Thrones.

While the lion of Lannister and the direwolf of Stark snarl and scrap, however, a second and greater threat takes shape across the narrow sea, where the Dothraki horselords mass their barbarian hordes for a great invasion of the Seven Kingdoms, led by the fierce and beautiful Daenerys Stormborn, the last of the Targaryen dragonlords. The Dothraki invasion will be the central story of my second volume, A Dance with Dragons.

The only thing that stands between the Seven Kingdoms and an endless night is the Wall, and a handful of men in black called the Night's Watch. Their story will be the heart of my third volume, The Winds of Winter. The final battle will also draw together characters and plot threads left from the first two books and resolve all in one huge climax.

These are from the 1993 letter. The series is supposed to have 3 parts, Stark vs Lannister war, Dany's invasion, and Others. The first part has stretched from one book to five and we're not even at Dany's invasion. How can parts two and three fit into only two books?