That's unfortunate. I would have them replace all 6 pieces. Most builders like to make the butt section of the rod from the lower half of the culm and the tip section from the upper section of the culm from the same culm that the butt section strips were taken. The theory being that you are basically recreating the culm that nature created. I would think that they would replace all six sections since they are a reputable bamboo dealer.
How bad were they crushed? It is fairly common for the culm to already have a split down the whole length of the culm whether it be a check split put their by someone or a drying split that occurred naturally. If it occurred naturally it will be irregular down the length of the culm as in it will be in different places between the nodes. I've had some tip section of culms that were split in numerous places. Any pictures? If they agree to replace all the sections, you might have lucked out because you'll have more to practice with.