Steve Helsley might know more, but as I understand it, Larry had no Clabrough ledgers to work with at all, nor did he know where any might have survived. I am sure he spent many years looking for them. He mentions this on the Acknowledgements page at the beginning of the book. The serial number tables in the book were based on the very large number of Clabrough guns he examined through the years. If he had possessed even a single ledger page from Clabrough or C&J, it would have been included in the book.
RIP Larry.