If you add an H2 bric to the page, it will not ordinarily have a custom class attached. However, if you change the font, size etc, a style called h2-style will be created automatically. This is because your changes are overriding the standard h2 style associated with your site.
If you add a second H2 style in a different bloc, and again adjust the font etc. another style will be created called h2-2-style. To prevent this from happening, don’t make any adjustments to the font size etc on the new heading. Instead, just apply the original H2 style to the new heading. Just type h2 in the classes field and you will see a list of classes beginning with H2. Blocs will ask you to confirm that you want to add this new freehand class to the heading you’re editing.
Any subsequent changes you make to that class will then be applied to all items where that class has been assigned.