".....altered and upgraded at French Arsenals" and "....repaired and overhauled" can mean several things. It sounds as if this means that they were used to make mixed pattern muskets and I do not think that is what Mr. Ahern meant at all, there are no mixed pattern French muskets that were made from random parts or altered to appear to be muskets of the new pattern.
To me it means that the muskets were repaired/refinished to bring them up to usable condition - as near new as possible. They also may have done minor alterations to improve them. Such as the changes done to make the 1763 model and the 1766 model which are very similar in appearance but are two distinct patterns.
This was not necessarily done for the use of the Americans, it was done while still in French possession for French use in the future. In other words, after their first term of service with French forces they were withdrawn to allow the new pattern muskets to be issued to French troops. The used muskets - most of which were still in serviceable condition - were cleaned, burnished and, if needed, repaired to get them ready for future service where needed. Any muskets needing serious repair were likely broken up for parts to be kept for future repairs to the earlier patterns if needed.
I hope this answers your concerns Ike, I think the auctioneer's blurb was simply written to glamorize a product that he/she knew little about but sounded good to the ear, especially to someone that wanted a musket to hang over a fireplace as part of a remodeling project. I hope Scots Jim will join the discussion.
