Dwarf should definitely go in the category of final-f words with variable plurals. |
While bare plurals are ambiguous between the two readings, indefinite singulars can only refer to a rule or a regulation. |
In noun compounds in English, the modifying noun may be singular or an irregularly inflected plural, but regularly inflected plurals are dispreferred. |
The reason why we use those words is because moose has an Algonquin word root and goose has a Germanic word root so the plurals are different. |
Using an apostrophe to show plurals of numbers, letters, and figures is optional. |
You can search for plurals or variations of word endings by using truncation. |