Intelligent Systems was quite smart and didn’t include the actual content for Waves 2~4 of the Fire Emblem Engage Expansion Pass in the currently available data. However, they weren’t quite thorough enough, because various files in the base game and Version 1.1.0 reference unreleased DLC.
This has happened in the past on numerous occasions, such as for Three Houses. I don’t have any experience of the development process, but I imagine DLC is developed in tandem with the main game, so it’s probably incredibly hard to fully separate the base game and DLC.
Of course, there will probably be spoilers, so be mindful if you wish to continue! This includes story spoilers.