Why were the S138 batches called one class?

Why did the Kaiserliche Marine group the very different S138 batches as one class?

Keeping one designation made repeat funding easier, and historians continued the documentary grouping even though the boats differed substantially.

Later S138 batches had different hull arrangements, machinery, weapons, and even an additional funnel. S182 makes the difference visible through its second funnel, rearranged masts, and altered hull. The funding argument is that retaining a familiar designation made repeat orders easier to present without inviting close scrutiny of the changes. Parts of the navy treated the batches as different classes, while historians continued the grouping found in the documents. In this reading, the shared label reflects administrative and political convenience despite substantial technical differences.