Thank you for the additional photos. I stand by my opinion that these are fantasy marks, and that the cup dates to the nineteenth century. Here is my logic:
-Maker's marks are read left to right, then top to bottom. On your cup, I read IBL, with the L being slightly larger and lower, therefore presumably the last name of the maker. Nevertheless, I looked at Nocq for the makers suggested by Sotheby's. First, Joseph Le Balleur, mark JLB, a rose. Le Balleur registered his mark on 29 August 1712, a bit early for your object. No end date is given for this maker. (See Nocq, v. 3, p. 43.) Next suggestion from the Sotheby's expert, Jean le Bastier, mark JLB, a rose. The le is lower case, unlike the first suggested maker. He registered his mark on 7 January 1699. He was still listed in 1715, but no end date is given. (See Nocq, v. 1, p. 77). Again very early for your object. Nocq unfortunately does not picture either of these marks, so we have to go by description alone.
-The maker was the first to stamp his mark; then he took the object to the maison commune to be assayed. The assay master stamped a mark that also served as a date letter. In this case the date letter is for 1753.
-Next stop was to the office of the fermier général (right next door) to have tax assessed or charged. On your object the charge mark is for 1726-1732. This does not correspond to the date letter. The maker returned the object to his workshop to be finished, taking it back to the tax office to be weighed again and to actually pay the tax owing. A discharge mark was applied when the tax was paid. The charge and discharge marks coincide on your object, but do not correspond to the later date letter. This is a real problem for me.
-Finally we have the picturesque slipper counter mark from 1774-1780. For those who collect marks, this one is sought after, yet it has no business being on a cup purportedly from 1726-1732. Maybe putting it there was someone's idea for making the cup more desirable?
The personalizations are family names, and are standard for cups which were often given as baptismal gifts, and handed down.
Wishing you the best in your further research.