Are there particular terms of use associated with Travelcards on Oyster? In particular, changeovers/refund&reissue. I see the National Rail CoC covers these in paragraph 37. Nothing is mentioned in either the TfL CoC or the Oyster Conditions of Use on National Rail.

If a Travelcard/Season is issued by TfL, rather than a TOC, the passenger has to be referred to them if they want a refund or change-over, and their rules apply.

Also, the NR CoC appears to explain refund & reissue situations, ie the new ticket must be at least as long as the old ticket when it was originally issued. So the general NR changeover process or pro-rata calcs for both tickets and keeping the same end date - is that just something offered, but not strictly written down anywhere?

The CoC version is slightly simplified from the actual process (and incorrect, given the new ticket is issued at the same time as the old one is surrendered, so starts immediately).

Change-overs are calculated based on the notional number of days the original ticket was valid, using the fares that applied when it was issued. One month is deemed to be 30 days long and one year is 365 days, regardless of whether it's a leap year.

So if the original ticket was valid for 1 month 17 days, the notional validity will be 47 days. If it was valid for 3 months 6 days, it'll be 96 days, and so on.

The value of the credit for the original ticket and charge for the new ticket use the number of calendar days from the date you wish the new ticket to start to the expiry date of the original ticket.

For a refund, on the other hand, you take the number of months and days the ticket's been used for, work out the cost of a ticket for that period, deduct it from the original price paid, then deduct a £10 admin fee.

There's a lookup table that gives the multiplication factor to be used in conjunction with the weekly price, though from 10 months 13 days you pay the same price as an Annual. There's also an associated formula to calculate the period factor, though it falls apart after 10 months 13 days:

p = 3.84m + 0.64f + 0.13d

Where p is the period factor, m is the number of whole months, f is the number of five day periods (maximum 6), and d is the odd number of days (maximum 4).

Cheers,

Barry