N:N relationship information is not included in Create/Update context. Only fields on the form can be passed into the Create/Update messages. If you need to get records from an association you should get the context.PrimaryEntityId and then do a retrieve
multiple inside your plugin. Or if you want to register your plugin when N:N records are associated with a record then you can register on the Associate and Disassociate messages as well.
P.S. I noticed you've asked a lot of questions lately, but have not been going back and closing them as answered. Please find the time to go through and close all of you questions as answered once you've resolved your problem. That way others can easily
find the answer when searching for similar problems, and also it's a way of thanking us for taking our time to help you.
Regards
Paul
If my response helped you find your answer please show your thanks by taking the time to "Mark As Answer" and "Vote As Helpful".
