Did captains always get credit for ships they sank?

They didn’t always think so. The first issue was that captains often overestimated the type of ship that was attacked, the damage done and the tonnage sunk. This estimate would be more accurate if the target was positively identified and then sunk. It helped if some of the wreckage with the ship’s identification could be recovered.

There were reviews of the claims by the individual captains by the submarine commanders for the area – the Central Pacific and the Southwest Pacific. Monitoring Japanese radio traffic could often confirm sinkings and the identities of those ships. That could increase the captains’ claims but most often reduced them

The final review, after the war, was by the Joint Army–Navy Assessment Committee (JANAC) which audited Japanese naval losses in WW2.This almost always resulted in captains losing credit for some ships sunk. Japanese records may not have been complete, particularly with regard to smaller vessels, those under 500 tons. Many submarine captains believed that they did not get full credit for the ships they sank since they were not confirmed in Japanese records. They would not get credit for vessels under 500 tons.