Thanks to all for further really valuable information. It is genuinely very helpful and greatly appreciated.

If I understood the agent correctly he did state that transferred miles did reset the expiry date. Considering the cost of transferring is over half that of purchasing ($25 vs $40 per 1000 miles) I would almost be expecting that to be the case.

He also appeared to state that if I purchased 25000 miles for my wife she would not then be able to purchase any more for herself. This is consistent with BA's approach. I can't comment on other programmes as I don't use any other airlines other than BA or Emirates any more than occasionally.

He was less than convincing however with English clearly not his first language. That is not meant to sound arrogant as I am the first to acknowledge my own poor language skills (common to many whose first language is English) although equally I am not working in an international call centre. Would greatly appreciate any further views on these two points. I think the others have been clarified.

Fairly sure the tickets I bought were not a special deal so hopefully some seats will be opened and available to me 15 days prior to flying.