Yes they differ between pregnancies in the same woman and in all women. This is because you implant when you implant with that pregnancy and your levels rise according to that and the speed at which that particular little embryo produces the hcg...
if two women ovulate the same day, its totally normal for one to get a bfp at 9dpo and the other not until 14dpo because hers implanted later and/or her body is producing/metabolizing slightly slower.
The range of what is "normal" is really broad for any dpo given that an implantation at 4dpo and an implantation at 8dpo are 4 days off in making hcg...
4dpo, for example, could go (from 5dpo on):
5, 7.5, 10, 12.5, 15, 17.5
8dpo, for example, could go (from 5dpo on):
0, 0, 0, 0, 5, 7.5
so while the 4dpo implanter is at 17.5, the 8dpo implanter is at 7.5 but they are both 100% perfectly healthy pregnancies (this rise is just an example and is not how *all women* rise but rather a fairly decent Idea... of doubling every 48 hours for the first few days)
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