At present I have 5 saved matches. These cover two savegames; three from one and two from another. I have found that I can watch the two from the second savegame but not the first three.

The only reason I can perhaps think of is that the savegame used an edited database (added a fictional team), whereas the unedited one used the original Demo database.

Savegame 1 was started post-8.0.1 (cannot view matches)
Savegame 2 was started in the Demo (can view matches)

Savegame 2 has been deleted, but as expected the saved matches still remain.

Can anyone see a reason for this? Is there something I have overlooked?

Which patch are you currently running?