Detaljerna varierade från berättelse till historia och var vanligtvis glansade över helt.
Detta är Lampshaded i den nya Cold Fusion som innehåller en rad olika orsaker (mestadels teknobabble och avsiktlig tredje partiinterferens), från en rad historier innan man medger att ibland minnen behålls:
‘Well, if he’s your future self, why don’t you remember all this from first time round?’
‘Does everything have to have a reason?’ Forrester asked.
‘Perhaps it’s magic.’
‘No, no,’ the fifth Doctor said, ‘the rules of time travel are very precise, and Mr Cwej here has a good point. Now, on both occasions that we met Omega, that was straightforward Blinovitch Conservation.’
‘That was true all three times, yes, but it doesn’t apply here,’ the other Doctor noted from underneath the console.
‘Yes, yes, I know that. Now, Zodin erased our brains with mind rubbers.’
‘I remember it well.’
‘But that hasn’t happened this time. The crashed TARDIS might have had misphased Relativity Displacers.’
‘It might,’ the seventh Doctor conceded, ‘but it didn’t.
‘Tachyon Backflush?’ the fifth Doctor suggested.
Chris sniggered. ‘Sorry – it’s just that it sounds rude.’
Forrester shook her head disbelievingly. Her Doctor stood, brushing himself off and taking his umbrella back from his past self
The fifth Doctor straightened. ‘There is another possibility.’
‘Go on.’
‘You do remember. You’ve remembered all along.’
The Doctor smiled enigmatically and tapped the side of his nose.
At the pre-arranged signal, Forrester knocked out the fifth Doctor with a swift blow to the back of the head.