From the Spotify for artists website:
( https://artists.spotify.com/faq/mastering-and-loudness#will-spotify-play-my-track-at-the-level-it’s-mastered )
“Ensure your master stays below -2db True Peak (TP) to be optimised for the lossy formats we use (Ogg/Vorbis and AAC), which, like all lossy formats, do not handle loud peaks well.”
“Generally, you won’t benefit from mastering louder than -14dB integrated LUFS due to Loudness Normalization. There’s no harm in doing so, but the tracks won’t play louder than that.”
The above means we now have targets to aim for. How I will amend my services to meet these is still in development, but it sure is great to know now!