Pyrox
Unable to answer "What is the reference number of this bus stop?" for https://osm.org/node/5538767461 via StreetComplete 38.2:

Many Arlington bus stops have 2 reference bus numbers, one for WMATA and one for ART. The "Real Time" number on the green sign can be used on the Arlington Transit site as a Bus Stop ID, meaning that this bus stop and the one across the street have multiple numbers. I'm putting pictures of the signs so someone with more experience can tag these properly.

Attached photo(s):
https://westnordost.de/p/77001.jpg