in 1881 he is in aldershot perm barracks. listed in the 45th sherwood foresters, 2nd battlion the derbyshire regiment.
So if I understand you right, his unit is listed as both of the above which is where your confusion lies?
There are in fact consistent and show the same unit (albeit he's possibly transferred battalion). Once you get to grips with the Army reforms of 1881 and the implications for regimental names/titles and amalgamations then it becomes clearer.
Prior to 1881 this was the situation:
Line infantry regiments were first and foremost designated by number (there were always a few exceptions though), and most regiments also had some kind of title/designation alongside the number. So for example,
- 45th (Nottinghamshire) (Sherwood Foresters) Regiment of Foot
- 95th (Derbyshire) Regiment of Foot
In the reforms in 1881, all these regiments lost their traditional numbers. In addition to that, in most cases two of the old regiments were amalgamated into one new regiment. This process happened to the 45th and 95th as an example.
So post 1881 this was the new situation:
- 1st battalion Sherwood Foresters (Derbyshire) Regt (new designation of the 45th)
- 2nd battalion Sherwood Foresters (Derbyshire Regt) (new designation of the 95th)
Later name changes then complicate the picture further. But Samuel was apparently only in the one regiment. The confusion arises as 1881 is just when the changes happened and everyone had to adjust to the new names.