Ipod Serial Number

I purchased a 5th gen ipod. The serial number ends with TXK. Apple identifies it as a 5th gen ipod purchased in 2006, but I keep reading that the serial numbers for 5th gen are the following:

The 5th Generation's serial number ends with: V9K, V9P, V9M, V9R, V9L, V9N, V9Q, V9S, WU9, WUA, WUB, WUC, or X3N. If you have the U2 Special Edition, the serial number will end with W9G

Why is mine different? Apple does recognize it. Does it still have the Wolfson dac?

Thanks!!