Whats the best 'Bareknuckle' book?

I am aware that there are usually several bouts on a card, but even at its peaks boxing didn't come close to having 250 or more bouts on the same day. Let's imagine turn of the century, Philadelphia having 6 shows on same night with 6 matches on each card and NY having 5 shows with 8 bouts on the card, that'd only make 76 bouts and those cities were the leaders in boxing shows back then, nobody else came even close to such numbers, but let's say 30 others cities around the world had their own cards on the same night, say 4 bouts on each card, it'd end up below 200 bouts on that very busy day (Philadelphia and NY clubs usually had one show per several days). You can look up recent results (which are obviously close to complete), even if you have both Americas, Europe, Australia and Asia having shows on the same day, it doesn't come close to 200 bouts.
Even most opimistic estimations shouldn't have more than 100 bouts/day, and that means about 4 million bouts during the last century and a half with boxrec listing 1/3 of them. 100 bouts per day is extremely optimistic guess in my opinion.

And sorry, but 1/3 undercard results is just your own opinion. Biggest number of bouts was taking place in major cities where boxrec editors usually have access to more than one local source to be aware of undercard bouts.