Several things... The genetics of fragrance are complicated... in a hybrid an individual may have it or not even if parents are fragrant. Even down to the species level, some individual cultivars may be more fragrant than others. Then timing... many orchids have fragrance only at certain times of day (or night). And it may be temperature-dependent as well. It is even dependent on one's nose... not only the plant genetics but the human genetics can get in the way. So fragrance is a rather ephemeral characteristic. The only way to be sure, is to buy at shows or nurseries where you can smell the flower in person.

I collect fragrant plants, including orchids. I have often pondered how much influence bee's and other pollinator's scent preferences have driven man's idea of what smells nice.

The one sure thing I’ve noticed by bringing orchids into the house only when they’re in bloom is that humidity is very important! If it’s low I don’t ever notice as much scent. In Michigan in winter or when the heat is on it really knocks the scent down. It also wafts much better in humid conditions.

Environmental conditions definitely play a role. I have a Prosthechea fragrans that I grew from a piece of a plant that I found growing on the roadside. I smelled the plant before I seen it, a really sweet honey and vanilla smell. It's since grown and bloomed for me for the last 5 or 6 years. Yet it's never displayed the same level of fragrance that the same plant did at higher elevations. Though it still smells pretty nice.
Oops, I just noticed I wrote pretty much the same thing in this thread about a year ago.

I have a Rlc Chia Lin 'Shinsu #1' AM/AOS (Oconee x Maitland) that the seller said is fragrant.
She is still a baby and at least a year and a half from blooming.
Now I can't wait.
Who said orchids teach patience?

I'm a night owl and so I have to say my brassavola have never let me down. The longevity of thier blooms are impressive, as well

rhyncholaelia dignyana, cannot go wrong there. also phal. schilleriana is strong, as are most brassias.

Any grocery store Miltiniopsis, people keep mentioning brassavola that is only because it is pleasant, but if you ever want anything that "punch" you in the face, it gotta be Miltoniopsis for me.