While Eau de Toilette contains 5-9% of perfume oil, Eau de Parfum usually contains 8-14%. Eau de Parfums therefore last longer and smell more intense.
Natural or synthetic fragrances?
Perfumes with natural ingredients often smell different in batches based on the source of the ingredients, while synthetic ingredients usually have consistency in their smell and lasts longer.
Notes and different smell after application?
Perfumes are often designed with top, middle and base notes, and designed to smell different based on the time after application. For example, some top note citrus scents smell stronger immediately upon application, while a lavender middle note may be sensed after some time from application as the top note evaporates.