Hi Mark,
It's your own personal choice really, whatever you feel comfortable with doing, but me perosnally, I would wait until I have all the relevant information such as amounts and dates etc, then you have concrete proof of everything, to help ensure that things go plain sailing. Your backdated payment usuaully just hits your bank account, before you receive the letter about this, so just keep a check.
Chris.
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
