Being allergic to some dogs and not other dogs is possible for some people.
Also some dogs with shorter hair may shed less and produce less dander which is what most people are allergic to when it comes to being allergic to dogs.
But you can also be allergic to dog urine and dog saliva as well and there's no way to know you'll not be allergic to a certain dog breed unless you're around them.
If you're allergic to dogs with longer hair that shed more then you might be able to live with a smaller dog with shorter hair that makes the dog more hypoallergenic.
The less the dog sheds the less likely you'll be allergic to that dog breed but then again you can be allergic to dogs urine or saliva.
My mother can be around small dogs that have shorter hair and shed less but when she gets around larger dogs with longer hair that sheds a lot she gets allergic to them.