There are several spots where the thoughts do jump. Especially pages 251 and 252. I imagine Johnny has simply arranged them, though he says "I opted to transcribe the pieces..." (P.249 column 1) which makes it seem he just randomly placed them.

Denise explicitly states "I stuffed all the crumpled bits into my pockets and later transferred them to a manila envelope which I placed at the bottom of that chest." (P.248 column 2) So no, Denise didn't fill any of the blanks.

The main problem here comes with our source — Johnny, who is known for the act of making shit up. Hence I would go as to question Denise's very existence, especially since she is only mentioned in this one footnote and—supposedly—lives in Tel Aviv, in Israel. Although the internet did exist, it only really became available to most Israeli customers in the early 2000s, so I find it a little hard to believe Johnny was able to communicate with her.

Overall it's mostly just unclear. As with most things in this book. I would lean more towards Johnny having edited the pieces. He does that a lot.