You see how there's still a little bit of space above the 6000 fpm climb and below the 6000 fpm descent (more on the descent)? Well, that's where the pointer would go, i.e. it would point above 6000 fpm climb, right to the very top of the grey bit and then it would stop. The actual grey bit is not added to when the limit is exceeded, just the needle goes further than the 6000 fpm line until it reaches the limit of the display, i.e. it is 'extended' beyond the limit line. Of course, the digital display will tell you what you're really doing.
Thankfully, never been there but the aerobatic aces of China Airlines and a few others have been, as I'm sure the NBO crew from BA would be able to attest
