Hello Marc,
Have just began reading Paul Dawsons work on Waterloo I think he corresponded with John Franklin about Legros and others mentioned would be interesting to know is conclusions in is work : The Struggle for Hougoumont - In the Words of Those Who Witnessed the Events of June 1815 by John Franklin pub 2016 would be interested in is conclusions. Have checked out the history of the 3e Regiment d'Infanterie de Ligne could only find a couple of paragraphs regarding Hougoumont.
Best regards as always,Tony