Let's look at the electoral track record of the Bernie coalition

[MH1]

6. I was surprised, and looked up Justice Democrats.

Wikipedia has 7 for 79 overall for JD endorsements (still quite low), then notes the 7 were D seats. So for flipping seats, your zero number holds up. (Just checking. I immediately thought AOC, but should have realized that was a solid D seat so not counted for your stats.)

https://en.wikipedia.org/wiki/Justice_Democrats

In the 2018 elections, 26 of the 79 candidates endorsed by Justice Democrats won their respective primary elections. Seven of these candidates won in the general election: Raúl Grijalva, Ro Khanna, Ayanna Pressley, Rashida Tlaib, Ilhan Omar, Alexandria Ocasio-Cortez, and Pramila Jayapal. All seven won districts already held by Democrats. Khanna and Jayapal were both first elected in 2016 before joining Justice Democrats, and Grijalva was first elected to the U.S. House of Representatives in 2002.