I think what's going on is that they're only printing the Sunday pages. Milton Caniff said that he wrote Sundays for the kids and dailies for the adults. Adults read the daily paper, so the dailies stressed character and plot. Kids read the Sunday paper, so Sundays stressed action.
But the majority of newspapers didn't print Sunday editions. For their benefit, whatever happened in the Sunday strip was summed up in a Monday caption. Creators tried several ways to be fair to both six-day and seven-day readers. Some made Sunday's events tangential to the story line. If someone's paper carried only the dailies, they'd never know they missed anything. Some had two different story lines running simultaneously, one during the week and the other on Sundays.( This practice proved confusing and most strips dumped it.)
Dann Dunn seems to use Sunday as a teaser to set up the next week's events. Since all the action happens in the dailies, the only thing we see in Famous Funnies is people discussing what happened "between the pages."
PS: You're right about Hairbreadth Harry. The strip had been around since 1907!! By this time it was hopelessly antiquated. It was finally permitted to die in 1940.
Link to the book:
Famous Funnies 026
