[Avodah] Mishpatim: shalem y'shalem

[Sholom Simon via Avodah]

There seems to be a lot of apparent "doubling" in Mishpatim -- in 
particular, I'm struck that there are many instances of shalem 
y'shalem, but also instances of just shalem.

I'm nowhere near fluent enough to see any patterns of when shalem 
y'shalem is used rather than the just shalem.

Is there a pattern?  Do mefarshim discuss this?

Thoughts?

-- Sholom