Indeed, some journeys do have a zero allocation, as well as these exclusions...
Booking deadline
4. Promotional fares must be bought a minimum of 7 days in advance of travel. Promotional fares are available to buy from 10 January 2023 until 23:59 on 17 January 2023; for travel from 17 January 2023 until 23:59 on 31 March 2023 (the “Term”).
Selected routes and limited availability
5. The following travel exclusion dates will apply:
4 and 25 February 2023 – Promotional fares for journeys to/from London Paddington to Cardiff, Swansea, Carmarthen, and Pembroke Dock are unavailable.
14, 15, 16, and 17 March 2023 – Promotional fares for journeys to/from London Paddington to Cheltenham Spa and Worcester via Swindon are unavailable.
20, 21, 22, 23, and 24 March 2023 – Promotional fares for journeys to/from London Paddington to Newbury, Bedwyn, Westbury, Taunton, Exeter, Plymouth and Penzance via Newbury and/or Castle Cary are unavailable.
6. 150,000 seats available as of 10 January 2023 (100,000 Standard Class and 50,000 First Class).
7. Promotional fares are subject to quota-controlled availability and will be valid for the booked GWR▸ service(s) only.
8. Promotional fares are available for selected journeys only, and are not available between every pair of GWR served stations.
9. Maximum of 9 persons per booking.
10. Promotional fares are subject to availability and may not be available at some peak times and are not valid with any other offer.
Other operators are also holding sales, so perhaps a co-ordinated
DFT▸ -driven approach to increasing ridership?
No word on what happens should another strike occur during this period however, so be careful when booking any accomodation & ensure it is refundable/cancellable