This is probably the solution, except when there are lots of networks within an organization with each a lot of users the the time waiting to fetch all the users, check if the exist, if not add them will add up soon and become a bit of a nuisance. Intended use is a webfronted for a service desk, which can be a bit impatient and refreshing the page whiel it is running. which poses more waiting etc. etc.
the problem lies within users that don't have an authorization in the network you are querying dont appear in the getuserlist, but when adding them an error is thrown (email taken) without knownig the userid (which is needed to update the authorizations). when using the Meraki dashboard to do the same users of other networks are displayed (but don't have authorizations).