Medieval Sword and Shield has been well received, but it is not the final word on medieval swordsmanship or on the I.33 system. Research into historical martial arts is like any other historical research. It is an ongoing process, which calls for open minded honesty, and a willingness to update your findings, even if that means admitting that you got some things wrong.
Since writing Medieval Sword and Shield, I have continued my research on this system. This has led to a number of changes in my interpretation and to some new insights into how the artwork, which lacks any perspective or sense of depth, should best be translated into physical movement. My latest thoughts on the system have been presented in a paper in the anthology Spada II, also published by Chivalry Bookshelf. Students of the I.33 system will find this paper a valuable addition to the book.
In closing, I must disagree with the comment by another reviewer that the use of Di Grassi's 16th century Italian footwork terminology was inappropriate. Di Grassi's footwork is not particularly distinctive. The basic forwards, backwards, angled and circular steps of Di Grassi are used in many other arts and in fact it would be difficult to imagine any sort of fencing system without most of these types of movement. The body mechanics of Di Grassi and the I.33 system are not identical, but that does not change a step forward into something other than a step forward. Di Grassi was unique in the detailed terminology he included to describe footwork, and that is why his terminology has become widely used in the historical fencing community.