Yes, you never know impi, George Chalmers might have signed on under an alias (as some others did), but then again, he could be the type of bloke who likes spinning a yarn, and said that he fought in the defence of RD, just to impress other people.
There might well have been quite a few chaps who liked to 'tell a good tale' down at the local, and some of these fellows who told convincing 'Zulu stories' may well have inscriptions on their headstones, saying things like 'Zulu war hero, or 'Rorke's Drift hero'. If they told convincing enough tales, it is surprising how many people would believe them at the time. That is why it's a good job that we have some good researchers who look into these sort of things, they try to get to the truth so that others can read their painstaking research.
If these 'new' RD defenders keep popping up, then people like Kris and Julian will have their work cut out in researching these men to try to get to the truth.