The WishList Member Import feature was developed to import New Members and not to Update existing member accounts.
If you have a member who is in three membership levels (Gold, Silver and Bronze) and you then import that member into the Gold membership level, then that member will be removed from the Silver and Bronze membership levels.
The WishList Member API can be used for additional importing options.
The WishList Member API and API Codex and can accessed using the link below. code and those are available using the link below: