Why a suggestion appeared
Suggestions come from the service intervals for your model, your mileage and what you have already logged. Accept one to plan it, or dismiss it.
A suggestion is never added to your history on its own — it sits as Suggested until you decide.
Accepting turns it into a planned entry with a due date or mileage; marking it done turns it into a normal logged record.
Dismissing one does not remove it forever; it can come back when the interval comes round again.