Great find Pierre!!!!!!!
you have guessed right it's the older UIC numbering, Jason has mentioned it at the first page of the topic
Divided to four series built by VEB WAGGONBAU BERLIN.

01 73 844 6 000-149, ex- 11 73 818 3 200-349, ex- 11 73 816 3 200-349, ex- SEK Ψπ 21001-21050, type Iehs-v

01 73 844 6 150-199, ex- 11 73 818 3 350-399, ex- 11 73 816 3 350-399, ex- SEK Ψπτ 21151-21200, type Iehs-v with braking hut

01 73 844 6 200-499, ex- 11 73 818 3 400-699, ex- 11 73 816 3 400-699, ex- SEK Ψπ 21201-21500, type Iehs-v

01 73 844 6 500-599, ex- 11 73 818 3 700-799, ex- 11 73 816 3 700-799, ex- SEK Ψπτ 21501-21600, type Iehs-v with braking hut