Acronyms: Plural, and then Singular

The acronym "SP" is first written in the document as: "contained in widely used or long-standing special permits (SP)."

Next it appears in the singular: "eliminate the need for numerous SP renewal requests."

Later it appears again in the plural form as: "submitted by the regulated community related to certain SPs and..."

Is this the correct usage for all three instances?

Solution 1:

It seems that the author meant for SP to represent "special permit" not "special permits." Given this, the second and third are clearly correct.

As for the first, perhaps it could have been "long-standing special permits (SPs)," but that might imply that the abbreviation always included a lower-case s, similar to PhD, or IPsec.

A better approach might be to rephrase the sentence so that the first abbreviation, denoted in parenthesis, didn't represent a plural form.

Solution 2:

@BrettQ, no I wouldn't put "SP" in parentheses twice in different forms, I would just make the first use of the initials match the grammatical use where they appear, in this case "SPs."