For those of us modeling German railways, we are confronted with the term “epoch” or “era“. You will notice these terms Epoch/Era I-VI (henceforth I will use the term “Epoch“) on manufacturers’ and dealers’ website to describe the railway period which the rolling stocks (locomotives, passenger and freight wagen, etc.) are associated with.

How strict does one follow the modeling epoch? Well, if you are a free-lanced modeler for example, where you mix-and-match whatever rolling stocks you acquired on your layout or you run some museum trains on modern-epoch layout, then it does not matter. Some stick to a particular epoch or transition epoch e.g. between Epoch I (Länderbahnen) to Epoch II (Deutsche Reichsbahn (DR), Deutsche-Reichsbahn-Gesellschaft (DRG))

In fact, I asked myself, how do these modeling epochs correspond to the real-world German railway periods. Bear in mind the modeling period was defined in NEM 800 (dt. Normen Europäischer Modellbahnen) and tied to define an epoch that apply to all European railways.

Below is my attempt to match the NEM800 modeling epochs to the actual periods in German railways history:

NEM800 Modeling Epochs	Period in German Railways
Epoch I until ca. 1925 Construction of the first railroads, development of steam locomotives, many private railroads with colorful rolling stock.	State Railways (dt. die Länderbahnen) (1835-1920) 8 kingdoms (dt. die Königreichen), Grand Duchies (dt. die Großherzogtum) and Imperial territory Alsace-Lorraine (dt. Elsaß-Lothringen) were collectively formed the pre-1920 Länderbahnen. The newly-formed Deutsche Reichsbahn in 1920 inherited most of the Länderbahnen rolling stocks.
Epoch II ca. 1920 until ca. 1950 Extensive standardization of construction and operating regulations, introduction of electric train operation, sporadic introduction of introduction of light signals.	Deutsche Reichsbahn (DR/DRG/DRB) (1920 – 1949 bzw. 1951) Within the Deutsche Reichsbahn period, there are 3 distinct “sub-periods” i.e. DR (1920-1924), DRG ((1924-1937)) and DRB (1937-1945). There was a short post-war administration by the Allied Forces and transition period between 1949 and 1951.
Epoch III ca. 1945 until ca. 1970 Reconstruction after the war and development of a modern rolling stock, traction changes through expansion of electric operation and diesel train haulage.	Post-war period (dt. Nachkriegszeit) (DB (BRD) / DR (DDR)) (1949/1951 – 1993) Post-war Germany saw a split between West and East Germany and within each separate country, their own railway administration.
Epoch IV ca. 1965 until ca. 1990 Large-scale completion of the traction changeover, introduction of an international lettering scheme for the rolling stock.
Epoch V ca. 1985 until 2010 Emergence of high-speed networks, promotional color scheme, start of liberalized access to rail networks, transformation of state railroads into joint stock into joint-stock companies with division into infrastructure companies and transport companies, separate for passenger and freight transport, which also operate outside the outside the traditional network.	Railway Reform (dt. die Bahnreform) (DB AG) (1994-present) DBAG was formed in 1994 as a joint-stock company and absorbed the former rail administrations of the East and West Germany.
Epoch VI ca. 2005 onwards In addition to the traditional railroad companies, numerous railroad companies (RUs) without their own infrastructure operate the existing railroad national or international passenger and/or freight rail networks with their own vehicles. with their own vehicles. Corresponding adaptation of the 12-digit UIC numbering scheme.

Abbreviations
DR: Deutsche Reichsbahn (1920-1924)
DRG: Deutsche Reichsbahn-Gesellschaft (1924-1937)
DRB: Deutsche Reichsbahn (1937-1945)
DB (BRD): Deutsche Bundesbahn (Bundesrepublik Deutschland)
DR (DDR): Deutsche Reichsbahn (Deutsche Demokratische Republik)
DBAG: Deutsche Bahn Aktiengesellschaft

In my blog, I will distinguish the Deutsche Reichsbahn, commonly abbreviated as DR, into their distinctive administrative periods to avoid confusion which Deutsche Reichsbahn I am referring to. The above abbreviations will be consistently applied throughout. Thus, the DR in 1970s will be referred to as DR (DDR) as compared to DR in 1922, which will be labelled as DR.

Development and key milestones in the German railways history (1835 – present) (Foto: Jimmy Low (c), Sources of emblems: Wikipedia, Google)

Abbreviations
K.P.St.E: Königlich Preußische Staatseisenbahnen (en. Prussian State Railways) includes Königlich Preußische und Großherzoglich Hessische Staatseisenbahn (K.P.u.G.H.St.E. (en. Royal Prussian and Grand-Ducal Hessian State Railways), later Preußische Staatseisenbahnen (Prussian state railways)
K.Sächs.Sts.E.B.: Königlich Sächsische Staatseisenbahnen (en. Royal Saxon State Railways)
K.Bay.Sts.B.: Königlich Bayerischen Staatseisenbahnen (en. Royal Bavarian State Railways)
G.Bad.St.E.: Großherzoglich Badische Staatseisenbahnen (en. Grand Duchy of Baden State Railways)
G.O.E.: Großherzoglich Oldenburgische Eisenbahn (en. Grand Duchy of Oldenburg Railway)
K.W.St.E.: Königlich Württembergischen Staats-Eisenbahnen (en. Royal Württemberg State Railways)
M.F.F.E.: Großherzoglich Mecklenburgische Friedrich-Franz-Eisenbahn (en. Grand Duchy of Mecklenburg Friedrich-Franz Railway)
EL: Kaiserliche Generaldirektion der Eisenbahnen in Elsaß-Lothringen (en. General Directorate of the Imperial Railways in Alsace-Lorraine) (note: there is no official abbreviation for railway in Alsace-Lorraine. The author abbreviated the official name for simplicity purpose.)

I hope my attempt will give you a good insight and help you bring realism into your German model railway layout.

Märklin has a product database sorted by epochs (or eras).