Single ply roofing guarantees, usually 15-20 years, cover manufacturing faults...

https://daisydustmaid.com/overlay-vs-full-replacement-for-a-single-ply-roof-when-does-overlay-make-sense/

Single ply roofing guarantees, usually 15-20 years, cover manufacturing faults but don’t always match the roof’s full service life of 25-40 years. Weather, maintenance, and installation quality all play a part