The codes on NES games typically start with NES, then a 2 letter unique code for each game, then the region code. So the Spy vs. Spy there is NES-SP-ITA, the US release of the game has a code NES-SP-USA, the UK release has a code NES-SP-UKV etc.
The GBR code on the Soccer game was a code used for the early black box games I believe. A lot of the early releases of these games in the US didn't have a code at all on them. There is an entry in the database for NES-SC-GBR, however this is a subtly different release.
Note that in Australia it's quite common to find ITA, GBR and UKV games as well as the AUS. The most likely explanation for this is that it was easiest for the Australian distributors to source some games being published in foreign markets than it was to publish them with AUS specific codes. Or an awful lot were sent over as Christmas presents
The codes AUS, UKV, GBR and ITA all represent the general PAL "region" of PAL A. So games with these codes will all work on NES's from those countries as they have the same lockout chip. You will also notice a capital A on your PAL games, this is because it's PAL A. PAL B is made up of Spain, France, Scandenavia, Germany, Holland and Sweden, and games from those areas won't work on an unmodified PAL A console. So while the video format is the same, the regions were seperated similar to the way DVD does it for market control I guess.
