Showing more text with JavaScript - Google and SEO aspects

I have a page with several lists. Each list has "Read more" button or link. When clicking the "Read more", additional elements are added to the list (sometimes by just changing the CSS, sometimes by loading more from the network by JavaScript).

For content loaded from the network Google says that I need to use History API.

Should I also use History API when I just reveal more text by modifying CSS?

When I reveal more, the URL modifies. So for N lists of M groups of items each, using History API would create M^N virtual URLs. Is such a big number of URLs good or bad for SEO? If it is bad, what can I do to avoid it?