Identifying supposed Imperial German tunic

[Fiore]

Hello friends,

I hope you can help me identify this purported WWI German field tunic, advertised as a 'late war' and 'unissued' example. Imperial Germany is not really my area (yet) and I would be grateful for any opinions. It does not seem to conform to any pattern of tunic I can see from my own basic research (cut, number of buttons etc.). Also the condition seems rather too good for c. 105 years old.

Thanks for looking!

[Verikauha]

That one-whole-piece backside cloth cut makes this tunic very very odd. Backside is super-simplefied like in great-coats.

Size stamp is correct-looking.
Aand ?A? ..18 ~ Stamp is Bekleidungs Amt... something BAK or BAR 1918.
K would be for Krieg, translated as "war-clothing-office". Forgot what R was for.

As germans were "uniform regulation Nazi's" this tunic might have served secondary clothing requirement for railway service, prisoner camps or other odd work-force related use.
I would guess this is immediate after-war coat