What is the etiquette about getting back books that you lent someone a long time ago? Asking for a friend.

My friend used to think that he would never forget which book he had lent to whom. But it was the disappearance of a prized hardback copy of Margaret Atwood’s The Penelopiad that undeceived me him. None of the people to whom he might have lent it remembered (or admitted) that they had it.
So he started to note loans down in a special notebook. But that has created its own problems.
For rereading it recently he saw that one book (signed by the author) had been lent to a friend a full five years ago.
Put yourself in this situation: various embarrassments can arise.
Does asking for it back after so long make you seem nerdish? Untrusting? In some way accusing your friend of carelessness? Best to have some specific reason for needing it, rather than just wanting to reclaim a piece of property for the sake of having it at home and not in their house.

Your friend might deny having got it. If it’s left at that, then the book will never be recovered. If the denial is challenged – well, do you suspect them of lying? Surely not – but that corrosive thought is in your mind now.
Do you ask your friend to check their shelves to make sure? If they do, and it can’t be found, why not? Have they in turn lent it to someone else? Have they lost it – left behind, perhaps, on some Spanish beach? Has a zealous spouse bent on clearing space given it to a charity shop?
If it is found – aha! They may claim (genuinely, let us hope) that it is their own copy. How to resolve this? Writing your name in your books is the obvious answer, but is that also nerdish? Something schoolboys do (or used to, when they still read books rather than looked at screens)? Obviously the worst thing you can do is to write your name in the book in the presence of the person you’re lending it to …
Let’s hope that this ownership problem doesn’t arise. It’s yours, and they’ve got it, and they’re giving it back. Do you make the mistake of asking them whether they liked it? For if they haven’t actually read it, how awkward …. Would you agree to their hanging on to it so they would sometime get round to reading it? Then you might have to go through the whole sorry performance again – but how can you politely say no?
This whole area is fraught with difficulty. And when you look round your house, and see books piled on windowsills and on the floor, because there is no more space on your shelves, then maybe that’s the perfect excuse for letting this particular sleeping dog lie.

Neither a lender nor a borrower be …