Hi Michael,
So, the zones 1-5 off-peak railcard cap is £10.15, as you found out on the 11th. If you have capped at £6.95 for zones 1-3, the most you will be charged extra is £3.20. You are correct that breaking the OSI did save you 30p, but the cap would have prevented the full £4.15 mixed mode fare being charged from either Seven Sisters or Ravenscourt Park. You could also touch on a bus at Victoria which would be free as you had capped and would also have broken the OSI. Unless you are certain that you won’t travel again I wouldn’t recommend using a different card because you lose the protection of the cap.
In the case of Ravenscourt Park you could have changed at Earls Court, West Brompton and Clapham Junction for a cheaper zone 2-5 fare of £2.45. You might even have got the direct Southern service from West Brompton to East Croydon.
As for the £1.00 refund, I have no clue. If it had been £0.95 then I’d think it could be the difference between the full fare from Victoria and the extension fare from boundary zone 3. However, I don’t think that discounted Oyster cards are put through the back office overnight, yet. You’ll have to ask the helpdesk and see if they can explain it.