Chris, I have never seen the box of this cartridge either, but I believe that this is an early variation of the .380 Revolver by G. Roth, which would explain the differences in measurements (other than extreme manufacturing tolerances). In some circumstances this is explained because some companies started with an outside lubricated bullet with heel and later changed to an inside lubricated design with an expanding base cavity or an entirely hollow base.
Also, even if I don’t think this is the case, if this is indeed an unknown 9.5x18R cartridge, then its G. Roth case number would be unknown as well, as there is no reported number for a 9.5x18R other than number 100, which is clearly described in catalogs as a .380 Revolver.
Here is a comparison of your specimen with another example with the same headstamp and a .380 Revolver by J. Roth:
Dimensions 1 (9.5 / * / GR / * /): RØ: 0.425, HØ: 0.374, MØ: 0.373, BØ: 0.373, CL: 0.719
Dimensions 2 (9.5 / * / GR / * /): RØ: 0.425, HØ: 0.375, MØ: 0.371, BØ: 0.375, CL: 0.702
Dimensions 3 (JR / * / 100 / * /): RØ: 0.413, HØ: 0.373, MØ: 0.370, BØ: 0.366, CL: 0.708
Dimensions 1 (9.5 / * / GR / * /): RØ: 10.79, HØ: 9.47, MØ: 9.47, BØ: 9.47, CL: 18.26
Dimensions 2 (9.5 / * / GR / * /): RØ: 10.79, HØ: 9.52, MØ: 9.42, BØ: 9.52, CL: 17.83
Dimensions 3 (JR / * / 100 / * /): RØ: 10.49, HØ: 9.47, MØ: 9.39, BØ: 9.29, CL: 17.98
For further comparion with other extreme measurements in .380, these are the dimensions of an early Eley example with copper case and “battery cup” primer (in millimeters only):
Dimensions 4 (no headstamp): RØ: 10.94, HØ: 9.61, MØ: 9.59, BØ: 9.58, CL: 17.64
And another one by SCB loaded with a hollow lead bullet (in millimeters only):
Dimensions 5 (SCB * 380 *): RØ: 10.90, HØ: 9.58, MØ: 9.57, BØ: 8.98, CL: 17.16
As you can see, if for some reason this 9.5x18R is something different from a .380 Revolver this is not clearly defined by its dimensions.
Regarding its designation, it seems that G. Roth considered that 9.5 mm was the equivalent to .380 from the 1880’s until c. WWI, and later changed to 9 mm. In the following excerpts you the see the designations used in 1886, c. 1910 and 1927, respectively.