I actually think that Henry did notice that no one was changing around him. I think that is why he didn’t have any friends in school because he was the only one to switch grades. Henry probably had just never met Cinderella, so that is why he didn’t know about her perpetual pregnancy.
I always sort of see it as things effect what is happening like the people who are not in a haze. So Regina would effect things in town and Henry would once he came. And maybe that they are more on a ground hogs day year where the year sort of repeats itself, but there would still be some differences because of Regina and Henry.