The duffel bag was rather expanded inside because, yes, there were more. It wasn't the complete collection, but never had Kingsley parted with them for longer than going to Hogwarts. And he always had his current scrapbooks with him, and there had been fewer to leave behind. They were his greatest work, in his opinion.
He hadn't been particularly trying to impress the younger Ravenclaws, though Kingsley saw it rather easily on their faces. He had been about to answer Kevin's question about seeing the other books when Su spoke. The way she spoke about them conjured mental images that, quite honestly, appalled him - books open to different pages, stacked on each other and spread around, with slight overlap. It was horrifying.
But Su was right about their usefulness in study. Kingsley studied them often. And he had been doing so around the time the potion he had heard of had been introduced. Kingsley hadn't known what it was back then. But he knew which day it had affected him. But the articles spoke the truth, and they had helped him. Logic. But it had to be done with proper care for the books. Kingsley knew them very well, but he doubted that even he could reproduce them, even with access to all of the newspapers he needed.
"The two of you can look at them, one at a time," Kingsley spoke clearly and firmly, "as long as you treat them properly - no food or drink, no ink near them." His eyes were serious, "They may indeed be very useful, and they should help us, but they are also my most valuable possession in the world." He did not hide that fact. That was why he had brought them to go to a safe home.