Oh yes I do fully believe she planned it for years, those spreadsheets with all the minor details. But I think some things she tweaked along the way, because PS and CoS both have Voldemort returning through a possessed vessel before it’s destroyed by Harry (Quirrell and the Diary).

All the other Horcruxes are magical artefacts and/or meant something to Riddle and are hidden in significant/secure places. But Harry can hear the diary like he could the others and it just doesn’t feel like a Horcrux when you re-read CoS.

I’m not saying there’s anything wrong with her changing things retroactively, I like the fact Harry destroyed one inadvertently without knowing what it was. Then again I may be wrong