I understand the standard rules. My questions relate to acronyms. If "USA" is possessive, should it be USA's (such as, "There are questions about USA's borders.")? Also, if a standard industry acronym exists, I believe no apostophe is needed to indicate the missing letters for the plural (example: Value Added Reseller is commonly referred to as a "VAR." If no possessive exists, then it should be VARs, and not VAR's. For instance, "Many VARs attended the conference."). Please advise if this is correct usage and if other rules apply to acronyms. Thanks.

I think you might be mixing up some basic terms there.
An acronym is an abbreviation spoken like a word. So, USA is not an acronym. It's an abbreviation. VAR could be one if you pronounce it "var" (i.e., it rhymes with "car").

Also, "Many VARs..." has nothing to do with the possessive form. It's just a plural. One VAR, Two VARs, Three VARs, Many VARs, etc.

The possessive form of VAR would be VAR's. For example, "The VAR's methods..."

Apostrophes can be used for the plural of abbreviations in some rare circumstances, but I would avoid using them if I were you. They really irk people.