Reward flight availability

Just wondering if I'm doing something stupid or if the website is taking the mickey!
I have been looking at reward flights to SFO. When I am on the homepage of the VS website I ask it to look for LHR to SFO return in any cabin. The availability grid comes up but even when there looks to be reward seats in all 3 cabins (eg 20th Aug is showing that just now) once I click on that date and it takes me to the next page there is actually only availability in one cabin??
I have tried various dates and the same problem sometimes occurs and I have tried every day for over a week now and again the same thing happens each time. Why is one bit of the site saying availability and the next bit says NO?!
Any advice would be greatly appreciated!
Many Thanks
Jo
I have been looking at reward flights to SFO. When I am on the homepage of the VS website I ask it to look for LHR to SFO return in any cabin. The availability grid comes up but even when there looks to be reward seats in all 3 cabins (eg 20th Aug is showing that just now) once I click on that date and it takes me to the next page there is actually only availability in one cabin??
I have tried various dates and the same problem sometimes occurs and I have tried every day for over a week now and again the same thing happens each time. Why is one bit of the site saying availability and the next bit says NO?!
Any advice would be greatly appreciated!
Many Thanks
Jo