Clarify packet number representation

draft-ietf-quic-tls.md

@@ -829,7 +829,7 @@ an output 16 bytes larger than their input.
 
 The key and IV for the packet are computed as described in {{protection-keys}}.
 The nonce, N, is formed by combining the packet protection IV with the packet
-number.  The 64 bits of the reconstructed QUIC packet number in network byte
+number.  The 62 bits of the reconstructed QUIC packet number in network byte
 order are left-padded with zeros to the size of the IV.  The exclusive OR of the
 padded packet number and the IV forms the AEAD nonce.
 

draft-ietf-quic-transport.md

@@ -2639,11 +2639,14 @@ other packets in the same UDP datagram.
 
 ## Packet Numbers {#packet-numbers}
 
-The packet number is an integer in the range 0 to 2^62-1. Where present, packet
-numbers are encoded as a variable-length integer (see {{integer-encoding}}).
-This number is used in determining the cryptographic nonce for packet
-protection.  Each endpoint maintains a separate packet number for sending and
-receiving.
+The packet number is an integer in the range 0 to (2^62)-1.  This number is used
+in determining the cryptographic nonce for packet protection.  Each endpoint
+maintains a separate packet number for sending and receiving.
+
+Packet numbers are limited to this range because they need to be representable
+in whole in the Largest Acknowledged field of an ACK frame ({{frame-ack}}).
+When present in a long or short header however, packet numbers are reduced and
+encoded in 1 to 4 bytes, see {{packet-encoding}}).
 
 Version Negotiation ({{packet-version}}) and Retry {{packet-retry}} packets do
 not include a packet number.
@@ -3297,7 +3300,8 @@ value of fields.
 
 ## Packet Number Encoding and Decoding {#packet-encoding}
 
-Packet numbers in long and short packet headers are encoded in 1 to 4 bytes.
+Packet numbers are integers in the range 0 to (2^62)-1 ({{packet-numbers}}).
+When present in long or short packet headers, they are encoded in 1 to 4 bytes.
 The number of bits required to represent the packet number is reduced by
 including the least significant bits of the packet number.