If a document has terms such as "silver" or "gold" in it, but without more detailed specification of the amount, the Gemara establishes the bare minimums (including for plural terms, including for currency exchange). Plus, the focus on the language is both precise and imprecise in the effort to draw conclusions. Also, the placement of statements in the lower portion of a document are determinant, so why write anything in the upper portion to begin with? Plus, the possibility of a letter missing - where only one missing letter is permitted.