it's the skill of using tools that'll stay with you,
you'll remember how to read datasheets and write code while referring to them but never the code itself. You'll still be able to do the same job.
It's happening to me too, but
I have actually put myself to test and noticed, now i'm more efficient. Though every thing I do, is done from scratch.
I think, our short term memory is increasing while long term memory is being overwritten. Also parts of memory not being read often gets erased.