Let's see if I can help you out here. First of all the letter stands for the company designation, then the title of the regiment (or sometimes battalion, but thats usually noted), the state the unit is from (or US for federal or "regular" army units) and the last is the type of unit (inf = Infantry, Cav = Cavalry etc...) So in your listing above the first would stand for Company G of the First Missouri Infantry Regiment, the second stands for Company K of the second United States Reserve Corp of Missouri Infantry. The USRC was a unit made up of soldiers recently discharged or invalided out of active service to form a "reserve unit" not a whole lot different from what happens today.
Now for the interesting find and question or two.
The Civil War Soldiers and Sailors system has a listing that matches the above for a Peter Robin not Victor.
The CWSS lists him with Compnay G 1st Mo Inf for 3 months enlistment in 1861. The USRC enlistment for 3 months 1861 and then there is a listng of him being with Co. A and Co. H of the 5th Cavalry regiment of the Missouri State Militia (second organization). CWSS does not list a Victor or V Robin. The Missouri state archives listing has a V Robin entered on a muster role from the 16th Enrolled Missouri Militia. This was a St. Louis Unit and I do not believe that the Peter Robin in the CWSS listing is the same person as the V Robin of teh 16th EMM. EMM and MSM service was not "federalized" service but were state units and generally service with those units did not qualify a soldier for a pension from the federal government.
Thus a couple of questions. Did your Victor ever go by Peter Robin? Second from where in the state did he come from? The 5th MSM Cav was reorganized from a unit primarily from Boone County and Central Missouri, does that match anything you know about your Victor?