Hi trying to change date of BA flight for our honeymoon. Our ticket was issued in October 12 for flights Sept 13;
We have had to change date of wedding and would like to fly Oct 28th now- our ticket only vaild til 18th Oct. We are willing pay the fees/charges and wondered of we changed flight now to may 13 then again to oct 13 will that be OK as our issue date will now be Jan 13?
i.e. if we change our flights now to May 13 is our date of issue now Jan 13 or does it remaining original date of October 12?

Only BA can answer this question because of the specific fare rules and conditions applying to the ticket. Phone them.

If you use the ticket for a new reservation then the ticket issue/validity dates do not change.

If you refund the ticket and get some money back to your credit card then the ticket would no longer exist and you would use the money to buy a new ticket with a new issue date.

I guess the third case would be most common: that you exchange the old ticket (plus cash) for a new ticket. You should expect the issue date to be the old date, but do as Gardyloo suggests and contact the airline.