I presume the PD doesn't change after you are an adult so you could reuse it in the future. My real concern is if I encounter some problems, if I got the exam

I presume the PD doesn't change after you are an adult so you could reuse it in the future. My real concern is if I encounter some problems, if I got the exam and glasses from one place, I can insist they fix it for me instead of arguing who is at fault.