There was a brief period of time before Faberge discontinued Tigress perfume, when the house marketed a perfumed bath oil of the same fragrance. It was then that I learned the staying power and longevity of perfumed bath oils over perfumes and colognes.
I purchased a 1/2 ounce bottle of Germaine Monteil's Royal Secret perfumed bath oil for my mother. Today, the oil has the same strength and the same unchanged scent as it did when I gave it to her. I gave her the oil over 45 years ago.
The length of time a perfume will remain 'fresh' varies from product to product. Also, the conditions under which it is kept play an important role in its longevity. However, if you are hoping to keep your favorite scent for a long time, consider buying it in the perfumed bath oil form. An added bonus is that it costs considerably less than perfume.
I should have added that perfumed bath oils are very concentrated. If you use two drops of your favorite perfume, when applying the same fragrance to the skin in the bath oil form, you probably would not want to us more than 1/4 drop.