There's no blackout dates in the fare rules, just a 120 day advance purchase requirement.
Fare rules & restrictions
Virgin Atlantic (VS) ZNAD3PMG MAN to BOS
General notes
BUSINESS EXCURSION FARES Z
Between UNITED KINGDOM and THE UNITED STATES FOR ROUND TRIP FARES
Category 4: Flight restrictions
THE FARE COMPONENT MUST BE ON
ONE OR MORE OF THE FOLLOWING
VS FLIGHTS 121 THROUGH 122
DL FLIGHTS 4343 THROUGH 4344.
Category 5: Advanced reservation/ticketing restrictions
RESERVATIONS FOR ALL SECTORS ARE REQUIRED AT LEAST 120
DAYS BEFORE DEPARTURE.
TICKETING MUST BE COMPLETED WITHIN 14 DAYS AFTER
RESERVATIONS ARE MADE OR AT LEAST 120 DAYS BEFORE
DEPARTURE WHICHEVER IS EARLIER.
There is a note to say that this particular Z class fare is capacity limited:
CAPACITY LIMITATIONS
THE CARRIER SHALL LIMIT THE NUMBER OF PASSENGERS CARRIED
ON ANY ONE FLIGHT AT FARES GOVERNED BY THIS RULE AND SUCH
FARES WILL NOT NECESSARILY BE AVAILABLE ON ALL FLIGHTS.
THE NUMBER OF SEATS WHICH THE CARRIER SHALL MAKE
AVAILABLE ON A GIVEN FLIGHT WILL BE DETERMINED BY THE
CARRIERS BEST JUDGMENT
and whoever wrote the fare rules can't spell judgement
