This does come up every so often so will share my experiences.

Few years ago. Brought IGFA rated 24kg from a big name shop 90 buck per spool
Brought 3 spools and did.my 3 50wides.

Month later in was setting and testing the drags for 8kg strike wanting 12 to 13kg on sunset. The line started breaking. So i did a bunch of tests and the most the line broke at was 13kg average was about 10kg some at 9kg Took the reels receipts etc back to the shop and we used new scales and a brand new spool of line and same result. Contacted the rep and supplier and they were not supprised in the least. Apparently plenty of charter boats had brought the line also.

Anyway i got all new spools of a different brand. And no.worries☺☺

I'll quote Bill Hall here as it's probably quite apt.
"Buying lines - , Watch out.
A number of brand line makers produce lines in two different qualities. One they usually describe as IGFA tournament line or something very similar, they may also claim it is to IGFA specifications.
If they say it is 37kg test, it usually breaks at say 36kg".

He then goes on to describe that there are also commercial brands that vary a lot on the breaking strand.
He suggests that as game fisherman we should know what line we are putting on the reel.
It's basically up to us to know. Fair point.

One thing that has a great impact is speed. If you have scales with the sliding ring that lets you know what it peaks at then its easy to see. Test the reel drag at walking pace as you normally would, then test the drag on the same setting pulling it as fast as you can. The difference is huge.