The confusion may stem from the practice of detailing private soldiers to signal duty instead of enlisting them in the corps. "Out of sight, out of mind," sort-of. Did Patti get a re-enlistment bonus from the 2nd at the end of their first year ('62), but enlist in the 154th -- a double dipper -- or is Cummins's memory at fault?
The reason for confusion, as with some other cases, is that Patti's detail to signal duty pre-dates the official establishment of the signal corps (Apr-May 62) and may have originated after Feb 62, when Beauregard "went west" and took along Cummins as his signal officer. Cummins -- indoctrinated and trained by E.P. Alexander -- functioned in that capacity initially for Beauregard and trained men who later received appointments or commissions in the corps, but he was never commissioned in the signal corps himself, doubtless because of the limited number of "slots" and the ceiling -- same as his then rank of captain. He gained his star in time as an "AAG Major."
Clagett went through a similar experience to Patti's, starting as a private detailed (from the 17th Va Inf) to signal duty "back east" under Alexander and earning his spurs "on-the-job," resulting in his getting one of the ten Alexander-endorsed first captaincies in the corps 29 May 62 and being sent west to report to Beauregard. Here our trio subsequently converge on the staff of Maj Gen D. H. Maury at Mobile -- Maj Cummins as adjutant, Capt Clagett as signal officer, Caro Patti as Signal Sergeant and Clagett's assistant. In an adjustment of Patti's pay, certified by Clagett and approved by Cummins, Patti was paid the difference between the monthly pay of a detailed private and the higher pay of a signal sergeant -- dating from Sep 1862. There should also signify the approximate date of his termination of any service with the 2nd Tenn (or 154th).
I realize that this doesn't account for his violin concerts, "ordered by Cleburne," but if you can absorb this, I'll tell you what happened to Carlo next!