Beginning in 1880, Germany issued this series of stamps containing the numeral values in ovals. Of note, they feature the word “PFENNIG” without an “E”, unlike MiNr. 31-36 and MiNr. 38.
The early (“I” suffix, up to about 1886) and late (“II” suffix, after about 1886) variants of these issue can be distinguished by the following:
“I” Suffix — up to approximately 1884, colors are more matte finish, and gum is yellowish with fine cracks. Up to approximately 1886, there are wide variations in paper and colors.
“II” Suffix — after late 1886, gum, paper, and colors are variable, but typically with somewhat glossy, rich colors in a smoother appearance and mostly white, glossy gum.