Personally, as far as content is concerned, SP, OVA and theatrical versions are all similar, but the playing forms are different.

SP is a special article, which actually means the same thing as foreign articles, and is usually displayed after the main text of the animation.

OVA is an original video animation, not a TV animation. It is sold on DVD. Generally, although the whole animation will not have many words, it will be released after a certain period of time, and the time span is relatively long.