You said that you'd use identical if not for the following problem:
People use identical in conversation to mean that A and B's properties are indistinguishable. Like identical twins aren't one and the same person, they are just indistinguishable for the most part.
As it happens, and as you anticipated when you said that 'there is some term in philosophy for it', philosophers did run into this same problem. Their solution was to invent the concept of numerical identity. Here is the opening paragraph of the article 'Identity' from Stanford Encyclopedia of Philosophy:
To say that things are identical is to say that they are the same. “Identity” and “sameness” mean the same; their meanings are identical. However, they have more than one meaning. A distinction is customarily drawn between qualitative and numerical identity or sameness. Things with qualitative identity share properties, so things can be more or less qualitatively identical. Poodles and Great Danes are qualitatively identical because they share the property of being a dog, and such properties as go along with that, but two poodles will (very likely) have greater qualitative identity. Numerical identity requires absolute, or total, qualitative identity, and can only hold between a thing and itself. Its name implies the controversial view that it is the only identity relation in accordance with which we can properly count (or number) things: x and y are to be properly counted as one just in case they are numerically identical.
So, using the example of linked lists, suppose we have a linked list a consisting of nodes a1-a4, a linked list b consisting of nodes b1-b4, and let's suppose that the last two nodes are common to both lists. In other words, a3 and b3 corresponds to one and the same chunk of computer memory, and similarly for a4 and b4. Then philosophers might say that a3 and b3 are numerically identical, by which they mean the following. When you point to nodes a1 and b1 and ask the question, 'How many nodes am I pointing to?', the answer is 'Two'. But if you point to nodes a3 and b3 and ask the same question, the answer is 'One'. That's why they are said to be 'numerically identical': they are identical (even for) the purposes of counting.
Unfortunatelly, the term numerically identical probably won't work outside of philosophical contexts. The problem is that non-philosophers will be tempted to think that when we say that two nodes are numerically identical, all we mean is that they contain the same numerical values, which can happen if they correspond to different chunks of physical memory whose contents are bit-for-bit clones of each other. Probably in non-philosophical contexts you'd have to say something like nodes a3 and b3 denote one and the same chunk of computer memory.