Its a long time between now and August. We won't know until Friday 10th August for certain who has been able to attend and who couldn't make it for whatever reason.
Plans can change. Final decisions can be reversed. The best you can hope is to ask their intentions right now, but I'm not sure if that actually helps much. If you are trying to decide if going to the grinder is suddently worth it because there is one extra slot then I expect the answer has to be No. One extra place does not change the risk/reward equation significantly unless you anticipate very very low attendance in the grinder. In which case you have probably already made your decision anyway.
Does that help?