Mild differnces in style don't really matter as they tend to share a few commonalities that unites it as a style. Every artist has their own form, but if they're drawing in a certain style, they will tend to adhere to the precepts of that style.
Basically, you can look at a peirce of art and say "Okay, this is a Renaisance peice". Then you can look deeper and say "This is a peice by X" by notating their own takes on the style.
Some of the unifications in Manga-style Sequential art include:
Intentional Simplification/detailing for Objectification - Manga style is a simplification for the most part, this is to create a better connection to the reader. Details in a character are used to create the idea of "other" ness or in objects, lend weight, importance and realism to them.
Eye Emphasis - The eyes, generally, take up a larger portion of the face than they do naturally. This is to better express emotions/express them more clearly as they are the "Window to the Soul". Actually borrowed from early United States Animation (Pre-WWII for the most part). Look at Betty Boop and early Bugs Bunny cartoons. Ozuma Tesuka (The "God of Manga") drew from these early imports. Before that, most Manga artists drew from their national heritage styles--and that popped up now and again afterwards (in one of my favorite Devilman pagespreads for one).
An Art of Intetvals - Less focus is given to action-to-action panel transitions in lue for Subjec-to-Subject and moment to moment transitons. In other words, there are more pregnant pauses with little movements or still shots of individual objects to set a scene.
I'm sure there are more, and I'd suggest picking up a copy of Scott McCloud's "Understanding Comics" for more info (though it's not exactly organized in a coherent manner, making finding info on a specific topic annoying at best).