The Hasbro people mentioned at BotCon last year that they "got the name back", so Hardshell was just a temporary alternative until they could reacquire the name in the last year.
It must have expired during the many years between Gen1 Bombshell was registered in 1984/85 (which covered ActionMaster Bombshell in 1991), and the first homage toy in 2008 (Robot Heroes figurine).

Now we just need Shrapnel back, who has been called Sharpshot and Skrapnel since Gen1, but it's too late for the Legends toy. Maybe when Kickback is released (as hinted by Hasbro at BotCon), a future three pack could have the original three names back.