Last time I was digging through the Google API documentation I noticed there is something that looks like a new method to receive incremental changes (i.e. changes sync last sync). Unlike the "changed-since" argument, this seems to be some token that we get on each sync, and we can then request changes that happened since this token was received. If that works, we should expose and use that token instead of the changed-since argument, which is basically search/filter, unlike the token, which is designed exactly for this.