In Europe, NES carts have either an 'A' or 'B' stamped on them. Both are PAL carts, and either will play on a PAL console (and most of them on a region-disabled US console), but the letters differ depensing on where the game was originally sold.
I *think* 'A' is the UK and Italy, while 'B' is just about everywhere else. [note: this isn't the same as the -UKV, -FRA, -SCN etc. codes in the part number. The same game may be released in different countries, all with an 'A' or 'B']
I'm not a Nintendo expert though, so if that's not quite 100% correct, I'm sure someone else can put me straight.