Oh, I agree. we all misremember, and/or produce our own mythologies about our distant pasts.
I think it’s just that she has similar ‘lapses of memory’ about far more recent things that supposedly happened, like the amount of money they had weekly in tax credits when they started the SWCP, which shifts about in interviews compared to what she says in TSP. Or when/if Moth fell off a barn roof.
Or how, despite him being a ‘townie’ and never having any farming experience outside of their hobbyfarming a few sheep and chickens on an acre in Wales, SW specifically shows him ‘remembering’ a farming experience he never had when he says ‘Do you remember how much equipment and livestock it took to farm a place this size?’ (To which she says ‘Not really, I think I’ve blocked it out. When we were walking I tried not to remember because thinking about home hurt too much…’ So she’s explicitly misrepresenting their repossessed home as a commercially-viable farm that had livestock and farm machinery, not an acre plot with a few sheep.)
To the point where one does find oneself wondering if the ‘memory lapses’ even of minor things like what she and TW talked about when they first met are a joint result of her having thoroughly rejigged timelines and invented cover stories, so that when she is asked an interview question, she’s not trying to cast her mind back to what really happened, but what she has said happened one or more times, which may bear no resemblance at all to reality.
Much harder to keep your story straight that way, because it’s easy to forget what you said previously. That’s why, if you need to lie, you’re advised to keep as close as possible to the facts. If you’re asked to account for your movements on the night of Saturday (when you shot your next door neighbour), use the real events of Friday night, when you went home, made dinner, and spent the whole evening watching films with your family, and just transpose them.