Dewey Dell isn't pregnant
Dewey Dell is oftentimes ignored by her family and forced to watch Vardaman, making her extremely naive and immature, and likely a reason why she got pregnant in the first place. In places where nutritional standards are poor due to poverty, it isn't that uncommon for one to miss a period or have it end abruptly. In fact, this troper has had a few times when she's missed her period and still got all the symptoms but blood. Dewey Dell, due to Parental Neglect
and likely having nobody to talk to immediately jumped to conclusion and believes
herself to be pregnant, assuming her fling with Lafe took place a few weeks to a month at most ago.
Anse knows the truth about Jewel's parentage
I mean, how could he be that stupid. He should've seen the resemblance. This is the reason why he quickly remarried after Addie died: it was to spite her for the affair.
Addie died from an STD she got from the affair
We never find out what killed Addie, be it old age or another disease. To many religious people, ST Ds
are punishments for infidelity and Addie would likely be no exception. And considering how Whitfield had no problem laying with a married woman, Addie might not have been the first person to sleep with him.
Darl is the father of Dewey Dell's child
In the 1920s South, it wouldn't be that uncommon for girls to be molested. And considering how naive Dewey Dell is, he could've easily taken advantage of her. When Dewey Dell sends him away, it is Laser-Guided Karma
for what he did to her. If you read the book with the interpretation that the pair have slept together or that he has in some way molested her, it puts everything into a new light. It could also explain how Darl knew Dewey Dell was pregnant, assuming she told him or he heard it through the grape vine.
Darl isn't truly clairvoyant
If Darl was clairvoyant, he would've likely known a lot of events in the story, like that the barn fire wouldn't destroy the coffin or that pouring cement on Cash's leg wouldn't help him. Darl is, instead, very observant and intuitive, and things that he guess happen like Addie dying are just coincidences. When he "sees" Addie dying, he probably just realized Addie was so sick that she wouldn't make it in time.
Darl inherited his powers from his mother
Addie seemed to speak from beyond the grave to state her perspective on everything, and seemed to know that Jewel would rescue her, even though she was dead. With most future seeing characters, she could've past it onto her son.
At the end of the book, he quickly remarries to a woman with the gramophone. Besides being a Jerkass, it would explain why he let Darl get taken away and didn't care that Cash had broken his leg: he was going to have a new farmhand with the woman.
Anse gave Addie an STD from his new wife
We have no idea how long it took Anse to find this woman, be it he found her
Anse won't care that Dewey Dell is pregnant
While it was kinda stupid for Dewey Dell to send Darl away, because he's the only person who knows about her pregnancy and could probably help her, had she asked. Still, considering one of his children can never walk again, another is sent to an insane asylum, and another isn't his, Anse won't mind that Dewey Dell is pregnant, as it'd mean he would have more hands to work the farm.
Lafe doesn't exist; he's Darl
Dewey Dell can't come to terms with the fact that her brother, Darl, raped her in the cotton field, so she made up the story of her and Lafe to cope. "Lafe" is Darl, and he gave her the ten dollars to get the abortion. it would explain she never went ahead with the shotgun wedding, as you can't marry your own brother, can you? It's never explained how Darl found out, unless he noticed the signs or Dewey Dell told him. When Dewey Dell punches him onto the cart, she's giving payback for raping her. Or, alternatively...
Jewel slept with Dewey Dell
It would explain she never told anybody. Her and Jewel are involved in an affair and when Addie found out, she got sick and died. Jewel loving his horse is because he's guilty he killed his mother.
Addie's chapter took place on her death bed
They say that when you're about to die, you see your whole life flash before your eyes. And the chapter is more or less Addie's past. So it isn't Addie from beyond the grave, but rather Addie thinking of her life over and deciding everything was alright. The chapter ends with her death.
Anse knows Jewel isn't his son
Anse purposefully withheld Peabody from Addie because he knows the truth