I have always thought that SS was buried and the killer either felt guilty that no one found her, or he didn't get what he wanted with her not being found so then he starting leaving the girls in a spot more discoverable. Just moo of course.
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It's hard to say if killers want their victims found or don't want their victims found depends on their warped reasoning. Some may like the feeling of having a secret no one knows about others might like the feeling of power scaring the wits out of an entire city.
In JR's case the reason she was found was that the Lillies near the body were bigger and drew the family to pick them. I am not religious in any way but I keep thinking the natural order of things (decomposing body) caused nutrients to seep into the ground and enhance those lillies or she may have still been there.