In the literature section there is a series for Kurt Jaeger books about pre-1871 coins.
Inside the series are these two books:
The two books cover the same set of coins with the same reference code for coins. (Often even the same pages.) But the 1957 book is Numisa reference code Jaeg 5 Bay and the 1968 isn't. It would be nice to say that the two books are different editions of the same work, but the “Part of” field is already used.
How can we connect these books together inside the series?