When I use one of your ISBNs from a previous post as test data, 9783642156298, at the end of running LC using only ISBN I get two more Identifiers for that ISBN:
oclc:913033698, oclc-owi:1059950222
LC uses the ISBN to get the oclc-owi from Classify, and then uses that value to get oclc from Worldcat:
https://www.worldcat.org/search?q=kw%3A1059950222.
The debug log shows where everything comes from.
LC uses A to get B, which is used to get C, which is used to get D & E.
To easily run Calibre in debug mode, run it from the command line or file as: "calibre-debug -g " and you will be able to watch what LC does in real-time.
DaltonST