Can “\parfillskip=0pt” shorten a short paragraph in plain TeX by two lines?

The decisions of TEX when it breaks a paragraph into lines are based on numerical calculations of badness values, line demerits, etc. With the help of the formulas that TEX implements, experts can decide questions about possible or impossible tasks. The question in the title compares the number of lines that TEX produces for a given text, if it is typeset with plain TEX’s default values, to the number that one gets with a single change applied to these defaults: \parfillskip is set to 0 pt. A problem of this type cannot be solved by the abovemen-tioned formulas alone although they help to find an assumed example in the simplest case of a three-line paragraph. But this example doesn’t respect plain ’s default values, as they aren’t captured in the formulas. Additionally, some assumptions about the TEX input are needed to show that the answer to the question in the title is “no” for Computer Modern Roman fonts of sizes 8 pt, 9 pt, 10 pt, and 12 pt.