month and day indicators; This watch indicates time, small seconds, powerreserve, moonphase and date.
The back of the real Lange watch doesnt say "REF 7850 ..." but would sport:
a case number (6 digits)
Manufaktur name "A. Lange & Sohne"
and place where it saw first light "Glashuette I/Sa"
Prob. another number too since it was a LE of (iirc) 101 pieces.
The dial should look like this: