Interesting. I always thought that once the sponsor is approved, that basically means that the applicant has (perhaps unofficially) been Approved in Principle, since without an approved sponsor, the applicant could never be `eligible'.
The only thing to do after sponsor approval is really criminality/security checks and medical...right?
AIP is a separate step that happens later. Sponsor approval just means that the sponsor themselves qualifies to sponsor (i.e. not on social assistance, etc.). AIP means the relationship and applicant have been reviewed and approved in principle.