Update SPEC.md

SPEC.md

@@ -171,13 +171,11 @@ Distribution across the encoding space:
 | Grain (slots 15–23) | 9 | ~40 avg | ~360 |
 | Bulk (slots 24–31) | 8 | ~40 avg | ~320 |
 | Other / Reserved (slots 29–31) | 3 | — | ~3 |
-| **Total active** | **32** | **128 max** | **~1,208** |
-| **Headroom** | | | **~907** |
+| **Total active** | **32** | **128 max** | **~1,906** |
+| **Headroom** | | | **~208** |
 
 Reserved ID slots are never assigned as printed tags. The Cultivar validates against the active dictionary. An unknown tag ID triggers graceful fallback — it never causes an error state.
 
-The **25% reserved headroom principle**: approximately one quarter of every slot range is reserved. New substrate or species additions consume reserved slots. A format revision is only required when reserved slots are exhausted.
-
 ---
 
 ## 5. Substrate Slots