Do all “errors” actually block rich results from appearing?

Most do, some don’t. Google’s rich-result rules are pickier than the Schema.org vocabulary itself:

• Hard blockers (rich result will not appear): missing required property for the rich-result type, malformed JSON syntax, @type not matching a valid rich-result type, image not resolvable, price not a Number, priceCurrency not a valid ISO 4217 code.
• Soft blockers (rich result may appear but with degraded features): missing aggregateRating (no stars in SERP but other parts of the rich result still show), missing brand on Product (price snippet shows but Merchant Listing eligibility may drop), missing author on Article (Top Stories ineligible but standard Article result still works).
• Non-blockers (rich result appears anyway, but the validator flags for hygiene): deprecated properties (Schema.org marks them but Google still honours them for backwards compatibility), non-canonical @context URLs (http://schema.org still works), excessive nesting depth (warns at ≥6 levels but works at ≥10).

The validator’s “Valid / Invalid” pill reflects Schema.org validity. The 0-100 score reflects rich-result eligibility. They’re different signals, a snippet can be Valid (Schema.org passes) with a score of 55 (rich result unlikely to appear). Watch both.