One principle governs all sources
Verified in, or held out.A field only becomes part of a post if it is present in the source. Truncated descriptions are dropped; missing scores are skipped; unverifiable facts are held. The feed is deliberately conservative — it would rather post less than post something it can't stand behind.
Adding a new source
To feed a new kind of post, add a section to gen-social-feed.py that reads the new data, cleans it, and emits items tagged with a new kind; then add matching templates. Keep the same rule: emit an item only when every field a template needs is verified.