How can inconsistencies in these sodium chloride solutions be explained? I'm entirely chemically-naive and am confounded when trying to convert $\ce{NaCl}$ brine concentrations to moles per litre.

The situation is that I'm performing linear multiple regressions using published data form multiple studies. Because the studies report their brine concentrations using different units I am trying to convert all of the concentrations into molarity (moles per litre). To do that I'm using the conversion tool at EndMemo - here's a screen shot:



But in more than one place in the literature people report different M values ... for example, below is an extract from one of the studies. Their M values don't match what I'm getting using the online converter (for example, 4 g/L $\ce{NaCl}$ is coming out as 0.068 M/L...hopefully I'm missing something very basic here?)


(Broseta D., Tonnet N., and Shah V., Geofluids, 2012, 12 (4), 280-294.)

As an aside, I'm not finding consistency with the unit symbols for Molarity and litre (sometimes they are capitalised, sometimes they are not...are they referring to different things or is this another example of inconsistency)?
example, 4 g/L $\ce{NaCl}$ is coming out as 0.68 M/L...hopefully I'm missing something very basic here


Yes, you are off by a factor of 10. 

4 g/L $\ce{NaCl}$ is 0.068M (0.068 moles per liter of solution).

As far as the journal article, I would used the 4 grams per liter value (and other grams per liter values) and convert to moles per liter properly and not rely on the 0.08 (small capital "M" l-1) value. 

If the value is critical to your research, email the corresponding author of the paper and and ask about it in a polite way.