This is normal for them.
Their ego is so fragile that they just can’t ever be the bad guy or wrong in any situation. I’m told narcissists have a huge sense of entitlement - so they think they can’t be wrong and that they always deserve to have or do whatever it is that they want.
I think their moral code is very ambiguous and needs to flip often to keep them feeling they did no wrong. This must be very uncomfortable for them.
I believe even if they do know it’s a lie at first - they quickly forget the original circumstances and then believe their own lie - they must always blame someone else.
I think because they exist with this aching void in their ego, they are never truly, deep down happy. They are always chasing something to fill this void - but it never does. Because they are always searching for something, they often change their mind about what they want. One minute they have a list of reasons why doing X is a good idea, the next they have a different list of reasons why doing X is NOT a good idea. This constant changing of mind and facts makes rewriting history seem quite normal to them.
They are like a miser who never has enough gold - they want everybody’s love and admiration - always, constantly - and it’s never enough.
If you leave them, it tells the world they are less than perfect. They can’t bear this so you are the one at fault, you are the one who must be blamed and you therefore deserve punishment. Ergo - you deserve to be lied to.
As you can probably tell, I’m recovering from a long relationship with a narcissist. I don’t feel sorry for him (yet- I’m trying do), but god knows I wouldn’t like to be him or sit inside his head, it must be fucking awful in there.