Good point.
Maybe they have been upgraded using self-sealing stembolts? 🤔

Don’t they phaser-weld? I know they use phasers to cut through bulkhead doors and stuff on occasion, but I feel like there are scenes where they use the same mechanism to weld things for repair as well.. Perhaps they made a point to only build with materials that could be repaired that way? And depending how phaser-welding works, that could be a wide range of materials.