Welcome to the boat mate.
Anyone that can come up with "mediocre english" ain't doing all that bad.
About the only time I've noticed not getting credit for a ship sunk is when it's at anchor in a harbor and didn't sink far enough to get credit.
One other time is if you have already sunk that particular ship before and hung around the same area and it re-spawned and you sank it again. No credit for the second time.
I don't recall ever not getting credit other than these two things.
Playing TMO 2.1 You should download the 2.0 to 2.1 patch.
Magic