Apple cannot make ALL iPhones meet IP67 specs [1] even though those devices are manufactured and sealed under factory automation and clean room environments. Their fine print clearly claims that resistance may decrease under normal wear. Anything exceptional, like cracked screens or back glass, damaged housings, missing screws, repairs etc. will definitely have an impact on water resistance.
[1] Your iPhone (ed. - iPhone 7 and later) is splash, water, and dust resistant and was tested under controlled laboratory conditions with a rating of IP67 under IEC standard 60529. Splash, water, and dust resistance are not permanent conditions, and resistance might decrease as a result of normal wear. '''''Liquid damage is not covered under warranty'''''.' - per Apple''
https://support.apple.com/en-ca/HT207043
What does IP67 mean?
Dust tight - No ingress of dust; complete protection against contact (dust tight). A vacuum must be applied. Test duration of up to 8 hours based on air flow.
Immersion (up to 1 m depth) - Ingress of water in harmful quantity shall not be possible when the enclosure is immersed in water under defined conditions of pressure and time. Test duration: 30 minutes. Tested with the lowest point of the enclosure 1000 mm below the surface of the water.