In many parts of its network, WPD has had to move to offering Category B ANM, because the level of accepted offers had already filled up to the Category Z limits. However, WPD does not yet have the Category B ANM system finalised, so it is likely to be a few more years until it is ready to be rolled out. If a connection offer says that it requires Category B ANM, it is possible that the connection of the site will need to wait until it is available on that part of the network.
In some scenarios, even the Category B ANM system will reach its allowed capacity (due to lots of accepted offers). When this happens, WPD will need to revert to issuing offers with conventional reinforcement, so increasing the capacity of the network by installing bigger overhead lines, underground cables and transformers. This, of course, comes with it a high price tag and long time delays.
Eventually ANM will run out of capacity in every location and DNOs will need to invest in the network. ANM is a great tool, but it is a short-term fix before a bigger and stronger grid is needed.