I am not exactly sure if anyone has ever bothered to find the maximum... most likely, it's 65535 or 255, 16-bit or 8-bit number. This would also most likely be the same for both the `Plus' and `Minus' attributes.
In the game itself, however, the values in the end fall between 1% and 99% (I might be wrong about the 1% `luck' factor). The to-hit is 0% when you're out of range, and 100% if you have the Talisman ability.
Any modders feel free to correct me on any of this, it has been quite some time since I dabbled in any modding