No, in general samples are not diluted or old. Sometimes, it makes a difference whether something is dabbed on or sprayed, the spray tends to have more power, also because, unknowingly, one tends to use more.
Longevity depends on many factors. Drier types of skin can literally eat perfume. Also, be aware of smell fatigue. After a while, a nose zooms out a smell, so you don't smell what you're wearing, but other people can (same as when someone stinks from sweat. One cannot feel oneself, but others can), so it's always worth to ask another person.
In the specific, Chanel no 5 eau de toilette is rather fleeting on me as well. The edp is much more long lasting. Shalimar lasts well on me, so I'm surprised on that.