[packman] libav versions

[packman at howorth.org.uk]

I just looked and noticed that I have three versions of all (AFAICT) of
the libav* packages. e.g:

libavformat56
libavformat57
libavformat58

Most of them have numbers 56,57,58 in the name. Some have 2,3,4 or 5,6,7

Do I need or benefit in some way from having all three? Or should I
just have the latest version (4.0.2.lp150...)?

If this is all documented somewhere, I apologize for not finding it.