As you progress the story in the Sinnoh games, the water level in Lake Verity will rise allowing you to Surf and reach the Verity Cavern. When this happens differs between DP/BDSP and Pt.
Zone 323 has nothing to do with it being early-game and only when Rowan's briefcase is present, but rather the differing water level. Riley's Riolu Egg can be hatched here without trading, as well.
Co-Authored-By: Billo-PS <63661653+Billo-PS@users.noreply.github.com>
Big thanks to @SciresM @sora10pls @Lusamine @architdate @ReignOfComputer for testing and contributing code / test cases. Can't add co-authors from the PR menu :(
Builds will fail because azure pipelines not yet updated with net6.