They have been identified through joint working with billing authorities and research, including detailed consideration of the features of relevant case law, over several years.
Maent wedi cael eu nodi drwy gydweithio ag awdurdodau bilio a thrwy ymchwil, gan gynnwys ystyriaeth fanwl o nodweddion cyfraith achosion berthnasol, dros nifer o flynyddoedd.