I think 324 is way to specific to be made up. It could be the real number of shows they played for Hybrid Theory until a certain point.
About 160 in 2001, and we have about another 110 for 2000 and earlier in our database. It comes pretty close considering there are a couple of 1999 label showcases and early 2000 shows we have no info about.
If you add the 23 shows from 2002 you easily get to the 324 for the entire HT touring cycle.
They either made up this number completely or someone did the math. In the Rolling Stone interview Phoenix estimated over 300 not 324, and that was at the end of 2001. I think it's also not unlikely that someone was keeping track and that they knew that LP played over 300 shows at this point (but probably not with Phoenix anyway). Whoever came up with the whole over 324 shows in 2001 seems not very smart, especially when you publish that "fact" in a book. It baffles me when people on Facebook for example believe this fact to be true because it's printed in a book, instead of just applying simple logic to it, that it's simply impossible for any band, especially an internationally touring band to play this many shows in one year without dying from exhaustion.