frieren mentioned that she lost to 11 mages with less mana than her in the past. perhaps its a foreshadowing that frieran might actually lose to ubel. then it will be fern who will defeat ubel. something like a student surpassing their masters or something.
The people who do the test looks quite young. .and Frieren party defeat the demon lord around 30 years ago so it's quite understandable. If the magic association did indeed changing very often like she said, any organized record would probably in a mess too.
It's been 29 years since Himmel's passing and 79 years since they returned from defeating the Demon Lord. The travel took them 10 years, so, not a lot of people alive from then.