Indeed, and it depends on what platform you’re promoting a story on. Truncated headlines are not likely to help you if the information that matters to potential readers appears after the truncation point. That point happens at different lengths on different feeds. The Medium mobile feed, for example, in the app, does not display headlines the same way the web browser version of Medium displays them.

Twitter, Facebook, Instagram, etc have their own headline length truncation points.

Also, in some versions of those platforms, the subtitle will appear in people’s feeds, but in other versions it will not. Medium stopped displaying subtitles in mobile feeds some time ago, and very recently stopped displaying them in web browser feeds too.

The long and short is that the headline has to convey necessary information before the truncation point, wherever that happens to fall on different platforms, without relying on the subtitle to convey information the potential reader might need before deciding to click.