Usually a mass mailing like that would be sent via a mailing house. the mailing house is given a mailing date or range of dates. They (RSSC) might have prepared the letters but then they go for mailing.

My guess is that they will come with the IRS 1040 packages that are being sent out to you. But I bet the IRS packages arrive first.

VOYAGER:
MC to FLL 11/07
MC/Dover 6/06
MARINER:
BCN / Ven 10/11
Alaska 2001|2006
Panama Canal 2003
NAV
Caribbean 11/06
Bermuda|New Eng/Canada 6/04
PG 5/05
OCEANIA
Nautica |Ist/Athens 6/07
Regatta|Baltics 6/08
Riviera 2013 Crossing -Istanbul to Miami