Welcome to the community!
I think whether or not a phone is able to access the APN settings on the SIM is dependent on the phone itself. Some devices are able to access the APN settings on the SIM. As mentioned in the other thread you in which you posted, the Sprint version of the S7 is CDMA-based (see here). Since CDMA networks doesn't use SIMs, they don't require APNs per se. However, APNs would be required for accessing the '3G' and LTE networks. It's possible those versions don't automatically access the APN settings on the SIM itself.
By the sounds of your other posts, you appear to have successfully added an APN and send MMS.
Hope this helps 😀