In my posts so far in trying to find more readable ways of presenting multiple series plots, I've tried multi-colors, and varying spectral maps. With multi-colors the lines may be easier to distinguish but harder to follow.
Eli, in a comment in the first post, suggested making curves respond to the pointer rolling over. This needs Java programming, which I can't do. But it occurred to me that an animated gif would achieve something of the same effect.
If each curve becomes, for a period, a continuous black line, then its path can be traced easily. Between times, the dots will separate out the local features. I'll switch to this more topical example - JAXA Ice extent: