Yevamos 15:8-9

Yevamos 15:8

If a woman went overseas with her husband and her son, then she returned and claimed that her husband died, followed by the son, she is believed (because she returns to her previous status quo). If she says that her son died, followed by her husband, she is not believed (because this creates a new status in that she requires yibum). However, her statement is taken into account so she performs chalitzah to the exclusion of yibum.

Yevamos 15:9

If a woman reports that a son was born while they were overseas, but that son died, followed by the husband, she is believed (because she didn’t have a son when she left so she returns to her status quo). If she says that her husband died, followed by her son, she is not believed (because this creates a new status for her, exempting her from yibum). However, her statement is taken into account so she performs chalitzah to the exclusion of yibum.