<<I am amazed at the quantity of inaccurate information on this subject that is available on the internet!>>
Where exactly on the internet....the TA site or the Lascaux website?
I quote (translated) from the official Semitour leaflet under the heading "Renseignements"
"Open all year except in January. Everyday except Monday in February, March, November and December. April to October open every day. Ticket Office in the town centre of Montignac (near the tourist office) from April to the end of September."
"Guided visits are offered in several languages outside of the planned dates and timetable : French, English, German, Dutch, Spanish"
Note: This was taken from a handout, not anything on the internet.
Perhaps, Growlerman, you were able to arrange your tour because you had a small group.
By going to the tourist office to get your ticket, you can still choose which tour (in which language) you wish to book for.
People on this site reply in good faith to requests for information based on their own experiences.
If you are referring to inaccuracies on other internet sites, then we can't be held responsible for that.