I'm thinking maybe the One Piece: Heart of Gold should stay as a stand-alone entry since it's a prequel to One Piece Film: GOLD. I don't know the content, though.

One Piece: Heart of Gold was a 1 hour tv special that aired in japan on July 16, 2016. I was not a stand alone movie but rather a special to drum up hype for the up coming movie. Also currently the specials section for One Piece (and many other anime) include movies in the specials section as a convention on database sites like the Movie DB. This is because many people who use the movie db for metadata for apps like plex keep anime franchise movies organized in the specials section of the respective anime rather than free floating in their moves section. Long running shows like Naruto and one piece have movies numbering in the teens for just one franchise not putting them with the show would clutter up their movies section.

Support for the Heart of gold being a special:

• Crunchyroll has it listed along with normal episodes instead of a stand alone spot
  
• Toei (the production company for one piece) press release stating the that it is a tv special
  

Support for the Movies being included in the specials section:

• One Piece Specials Section on The Movie DB
  Episodes 2, 4, 6, 8, 11, 13, 15, 16, 17, 19, 21, & 26 are all movies that received theatrical releases (you can cross reference with this wiki which provides sources)

Also I guess Flim Gold should also be included with the specials too considering it is the only One Piece movie currently not listed in the section