fix: revert specVersion to optional in tier-check details, remove stale table

Author: felixweinberger

.claude/skills/mcp-sdk-tier-audit/references/tier-requirements.md

@@ -32,23 +32,13 @@ Source: `modelcontextprotocol/docs/community/sdk-tiers.mdx` in the spec reposito
 
 ## Conformance Score Calculation
 
-Every scenario in the conformance suite now has a `specVersion` field indicating which spec version it targets:
+Every scenario in the conformance suite has a `specVersion` field indicating which spec version it targets. The valid values are defined as the `SpecVersion` type in `src/types.ts` — run `node dist/index.js list` to see the current mapping of scenarios to spec versions.
 
-| specVersion  | Meaning                                                | Count toward tier score? |
-| ------------ | ------------------------------------------------------ | ------------------------ |
-| `2025-03-26` | Legacy spec (March 2025)                               | Yes                      |
-| `2025-06-18` | Base spec — Tier 2 baseline                            | Yes                      |
-| `2025-11-25` | Current spec — Tier 1 baseline                         | Yes                      |
-| `draft`      | Unreleased draft spec features                         | Listed separately        |
-| `extension`  | Optional protocol extensions (e.g. ext-auth, SEP-1046) | Listed separately        |
+Date-versioned scenarios (e.g. `2025-06-18`, `2025-11-25`) count toward tier scoring. `draft` and `extension` scenarios are listed separately as informational.
 
-The `--spec-version` CLI flag filters scenarios cumulatively for date versions:
+The `--spec-version` CLI flag filters scenarios cumulatively for date versions (e.g. `--spec-version 2025-06-18` includes `2025-03-26` + `2025-06-18`). For `draft`/`extension`, it returns exact matches only.
 
-- `--spec-version 2025-06-18` includes `2025-03-26` + `2025-06-18` scenarios
-- `--spec-version 2025-11-25` includes all three dated versions
-- `--spec-version draft` or `--spec-version extension` returns only exact matches
-
-The tier-check CLI output includes a per-version breakdown alongside the aggregate pass rate, and groups `draft`/`extension` results separately as informational.
+The tier-check output includes a per-version pass rate breakdown alongside the aggregate.
 
 ## Tier Relegation Rules