General Notes

Ancestral Roots has a death date of 904 for Theobald.  However the Encyclopaedia Britannica states that Theobald of Blois, who is his son, was b. circa 908; and Theobald defended Chartres against Rollo later Duke of Normandy in 911; so Ancestral Roots is either wrong or has a misprint.  If a misprint, then either 914 or 940 is the more probable death date.  His son became active in 940, so maybe that was when he died.

The following is a copy of a post by Gayle Wilson to soc.genealogy.medieval:

From: Gayle Wilson (gayle@@inforum.net)
Subject: Re: Thibault I Count of Blois
Newsgroups: soc.genealogy.medieval
Date: 1997/03/11

Hi Jerry!

Permit me to explain the story, as I understand it, primarily from J de Petigny and Professor Launay's Historie Archeologique Du Vendome, I, pages 121-122, Academie des Inscriptions et Belle Lettres Chartes et Diplomas: Receuil Des Actes De Charles III, page xx,  and Pere Anselme's (Pierre Guibors) Histoire Genealogicue et Chronilogique des Rois de France, II, pages 33-34.
Theobald, Viscount of Troyes, married Richelde, the daughter of Hugh Aquitaine, Count of Bourges and his wife, Rothaut (the daughter of Charles II 'l'Chauve' ['The Bald'] King of France and Ricardis Buwinis Amiens, although some list her mother as Ermentrude Orleans, but that is topic for another day...) circa 886.  As a result of this marriage, Theobald (Thiabald, Thiabault, etc) became guardian of Richelda's younger brother, Hugh, and was given the territories of Blois and Chartres in appreciation of this service.  Shortly thereafter, a marauding band of Norman pirates, who had recently taken up residence on the banks of the Seine, attacked Chartres. 
These brigands, led by a certain 'Rollon', were more than Theobald could handle on his own.  Theobald sent messangers to his wife's cousin, King Charles III 'The Simple', Conrad, Duke of Bourgogne and Ebles, Count of Poiters, appealing for assistance.  The castle had been under seige for some time, when Joscelin, Bishop of Chartres, perched within the castle ramparts, saw clouds of dust rising in several directions on the horizon.  Help was on its way!
The counter-attack was led by King Charles; the Norsemen were forced to lift the seige.  King Charles and the renegade Rollon, or Rolf, had a little chit-chat and a diploma thereafter referred to as the Treaty of Saint Clair-sur-Epte was eventually drawn up, including an agreement by Rollon to revert to Christianity and be a good boy with a tight leash held on his followers.  For these concessions he was given the area that would later be called Normandy to govern, and the hand of the fair Princess, Giselle, daughter of King Charles.
So, you can see that there is a little glimmer of credence to the information you were given.  Giselle, the wife of Rollo, was cousin to Richelde, the wife of *a* Theobald of Blois.  This person is the father of the Theobald in your query, Theobald I 'le Tricheur' (The Cheater) Count of Blois, who was indeed husband of Luitgarde Vermandois and father of Eudes (Actes de Comtes De Namur 946-1196 (Rousseau) XXXVII;  House Tirel 80; Vanderkindere79-86; Pere Anselme I 49; Derniers Carlovingniens 141; Histoire de Cambray et Cambresis III 970; Histoire Archeologique Du Vendomois 147...etc).  Hope this helps.

May your roses always bloom in the Son,

Gayle Wilson