>> I've certainly never experienced anything close to a normal crew shortage and I've never heard of anyone who has
Generally, it's only likely to ever happen if you go on a building spree really early, and/or forget to mark your civilian vessels for conscript crew, and end up staffing a load of freighters with Naval crew for no real reason. Even if you do run out of Academy trained crew, IIRC (and I may not), any remaining crew slots are assumed to be conscripts, with the lower base CG that implies, so it's not like you'd get a message that a ship can't be built due to lack of crew at any point, you'd just build some with terrible starting CG stats