ipip-0412: clarify dups CAR parameter

src/ipips/ipip-0412.md

@@ -56,9 +56,9 @@ CAR flavour is returned with the response.
 The proposed solution introduces two new parameters for the content type headers
 in HTTP requests and responses: `order` and `dups`.
 
-The `order` parameter allows the client to indicate its preference for a
-specific block order in the CAR response, and the `dups` parameter specifies
-whether duplicate blocks are allowed in the response.
+The `order` parameter lets the client specify the desired block order in the
+CAR response, while the `dups` parameter determines if a block is sent multiple
+times when it appears more than once in the requested DAG.
 
 ### Signaling in Request
 
@@ -95,15 +95,23 @@ The `order` parameter accepts the following values:
 
 The `dups` parameter specifies whether duplicate blocks (the same block
 occuring multiple times in the requested DAG) will be present in the CAR
-response.
+response. Useful when a deterministic block order is used.
 
 It accepts two values:
-- `y`: duplicate blocks are allowed
-- `n`: duplicates are not allowed
+- `y`: Duplicate blocks MUST be sent every time they occur during the DAG walk.
+- `n`: Duplicate blocks MUST be sent only once.
 
-When allowed (`y`), light clients are able to  discard blocks after
+When set to `y`, light clients are able to  discard blocks after
 reading them, removing the need for caching in-memory or on-disk.
 
+Setting to `n` allows for more efficient data transfer of certain types of data,
+but introduces additional resource cost on the receiving end.
+
+If the `dups` parameter is not present in the `Content-Type` header, the
+behavior is unspecified, and the CAR response includes an arbitrary list of
+blocks. In this case, the client should assume `n` as the default, but ignore
+duplicates if they are present.
+
 <!-- TODO: do we need a  parameter for inclusion of identity CIDs?
 It seems to be only relevant in Filecoin due to legacy hiccup:
 https://github.com/ipfs/specs/pull/330#issuecomment-1274106892 -->