回複：如果回國簽H1B，剛回到美國，早先申請的H4也批下來了

If the H-4 was COS, it is deemed void. When H-4 was EOS, you changed to H-4 after you were admitted in H-1. In such case, when you go to Canada and get back, CBP will apply 30 days policy which gets you H-4 I-94.