Dragon Ball/Z/GT special episodes, and OVAs

I have a question regarding the special episodes and OVAs of the Dragon Ball franchise. In many other franchises, this type of episode is categorized as a series special, but here, each one has its own dedicated page.

My question is: is this the correct approach? Or should these episodes be listed as special episodes within their respective shows?

Here is a list of all of them:

Part of Dragon Ball:
Dragon Ball: The Return of Son Goku and Friends!
Dragon Ball: Plan to Eradicate the Super Saiyans (Although this appears to take place within the "Dragon Ball Z" continuity, it is simply titled "Dragon Ball", and in any case, that division does not exist in the original manga.)
Dragon Ball: Episode of Bardock

Part of Dragon Ball Z:
Dragon Ball Z: Bardock - The Father of Goku
Dragon Ball Z: The History of Trunks

Dragon Ball Z Side Story: Plan to Eradicate the Saiyans

Part of Dragon Ball GT:
Dragon Ball GT: A Hero's Legacy