Cross Country Trains are also striking THIS Saturday (due to the RMT), 19 August; also 9 September- as well as on the two National Strike Days of 26 August and 2 September.
I don't know how this crept under the radar for this forum, but there you are- details of the very restricted service being provided on 19 August are here- https://www.crosscountrytrains.co.uk/travel-updates-information/changes-to-train-times/industrial-action
For the other 3 Saturdays will be published in due course.
Tickets can be used the previous day or on the following Monday without having to be exchanged for new tickets.