Facing a similar case of TFL SJPN to @lanaarcher just received the letter.
In my case, I:
- Put both my pass and my grandmother's pass in the same oyster wallet
- Intention was to drop off her pass as she had no way of coming back with my uncle at work
- Did not have my phone as I was mugged in April ( TFL event took place in July), didn't not purchase new phone to avoid search costs during exam season - hence situation was time-sensitive to complete the task