Ever seen one of these before? It's the complete book but in loose pages for the XB31 for 1945. The BSA ledgers seems to indicate that no XB31 has been sold in that year or maybe just one. That would have been frame number XB31 134 with engine XB31 101 and it seems to have happened on the first of August 1945.
Maybe it is in loose pages because it is not an actual book yet.
The stamp says "proof", which in printing means it is the first evaluation copy for inspection,
Before the actual edition release.