The stored checksum is the complement of the folded sum. This is the payoff for the checksum field deferred in the first packet book.
Why the final value is inverted
After folding, the checksum field stores the one's-complement of the sum. That stored value is what makes verification fold to all ones later.
folded=0x4e19
Take the complement
The folded sum 0x4e19 complements to 0xb1e6. That is exactly the checksum field Book 1 showed and deferred.
∼0x4e19=0xb1e6
The deferred field is now computed
Book 1 displayed 0xb1e6 as a field. Here the table recomputes it from the bytes.
checksum=0xb1e6
Summary
The checksum field is the complement of the folded one's-complement sum. Error detection over the exact bytes; timing/throughput is not modeled here.
checksum=0xb1e6