you need to know 3 important parts of the os, kernel, desktop environment and iso used to install
you downloaded the iso so you know what is your base, this base if you update using synaptic is not really important because pclinux updates everything(if you don't do selective updating and end breaking the system)
the kernel, you can open a console and write uname -a and see what it reports as the kernel in use
the kernel is not updated automatically to avoid problems
the os, you can verify in kde control center, in gnome i can't remember but each de has a proper way
if you are updated, you have the latest pclinux available