I dont believe its trip that does them but the guys in london.
With regards to the damage, there is another way of looking at it, they did the job they were suppose to do! Not all falls are the same and some may crack the knee pad, it just depends on whether it was a minor fall etc.
If they replace it is good of them, but if they don't as a seller I would understand.
On the subject of Knee / Shin pads, there are currently delays with our ones, so in the mean time I ordered a set of eBay for my nephew, there was a link on the forum somewhere, in the pic they looked identical to ours but when we recieved them you could tell they were of a very diffferent quality and no where near the same as the Pit Dirt ones. So if you have seen the Pit Dirt ones in "flesh" it may be a better idea to see if you can try and match the quality in an actual shop.