Consider this repro: https://github.com/HalfdanJ/lit-element-starter-ts (recommend opening a github codespace to get a stand alone fresh install of the VSCode plugin, with only local configuration)

With a same-project import of some-element, we still get an unknown tag warning unless it's added to the HTMLElementTagNameMap, and even if it is we get an unknown attribute warning unless we add an @attr jsdoc tag to SomeElement. It's as though the analyzer can't see the @property or @customElement decorators