Mouin sent me this: "Your question about how HRW would respond if it had no
direct in situ evidence of ammunition use by Israel (vs. Syria) need not
be rhetorical. There's an established track record.
Just look at their coverage during Operation Cast Lead. In that case, it actually hid behind its inability "to
conduct full investigations into alleged laws of war violations by
either side because of Israel’s continuing denial of access to Gaza", to
avoid drawing
conclusions. Saturated television coverage of white phosphorus raining
down on the Gaza Strip, and the resultant corpses, were effectively
dismissed as mere hearsay."