It seems to be fading alot faster than normal pbt should.
The PBT itself is not fading. It's the way the legends are put on, which on those are laser etched or pad printed, causing them to rub off/fade.
The only legends that won't fade on PBT are deysub, which cannot be a lighter legend on a darker cap. So since yours look to be gold on black or so, those are not dyesub.