I found two 20th Century references to this rose giving the introduction date as 1848; one reference gave the breeder as Victor Verdier, and it seems likely that 'Comtesse de Ségur' was meant. The other reference said that the rose was put into commerce (not necessarily bred) by Eugène Verdier; again, the 1848 date probably points to confusion with 'Comtesse de Ségur'.

Since I couldn't locate any references to 'Comtesse de Séguier' prior to 1861, my assumption is that it wasn't released until then.

On p.39 of the 1906 edition of Nomenclature de tous les noms de roses, there are two listings for 'Comtesse deSeguier' followed by one for 'Comtesse de Segur':

2.535 Comtesse de Séguier HR V. Verdier, 1848, rouge vif
2.536 Comtesse de Séguier HR Samson, 1861, rouge vif
2.537 Comtesse de Ségur Centifolia V. Verdier, 1848, carné très frais

The other reference is from the June 1902 Journal des Roses featuring an obituary of Eugène Verdier, with a list of all the roses he put into commerce (p.83):

NÉCROLOGIE - EUGÈNE VERDIER
Rosiers Mis au Commerce par Eugène Verdier.
Comtesse de Séguier: Hybride Remontant, 1848.

Virginia