score:3
You applied for an extension of your H4 status. Status is something which only exists while you're in the US. When you left the US, you ceased to have any status.
Except after trips of less than 30 days to Canada or Mexico (in which case you can enter on Automatic Revalidation), the next time you enter the US, you must enter on the basis of a valid US visa. This could be an H4 visa, or some other visa, and you will be admitted to a new status from scratch, with the status having the same category as your visa, and for a new duration based on the rules of admission for that visa. (Or if you are entering on the Visa Waiver Program, you will be admitted to that status from scratch. Or if you are a Canadian citizen, you don't need a visa, but everything else I said about being admitted to a new status from scratch applies.)
Assuming that the officer on your next entry decides to admit you, the new status and duration you get is not related to what status you had during your past stay (and whether it was extended and/or changed); it is simply based on the visa you present on that entry. There is no point to approve or deny an Extension of Stay or Change of Status application after you have already left the US, because the decision makes no difference -- you are going to be admitted on the basis of your visa on your next entry anyway, not on the basis of your previous status. (And you do not accrue unlawful presence while a timely-filed, non-frivolous Extension of Stay or Change of Status application is pending anyway, so an approval or denial after you left makes no difference for the purposes of unlawful presence either.) Normally, they would automatically consider your Extension of Stay application abandoned if you left while it was pending; the fact that they approved it is probably an oversight. But again, as I explained, the approval doesn't matter.
Your ability to seek entry into the US into H4 status only depends on you having an unexpired H4 visa (or being a Canadian citizen with no visa), and your spouse being in H1b status. It does not depend on whether your previous Extension of Stay application was approved, denied, or abandoned. Yes, you can use H4 status for visits, long or short.