I think this question should be rephrased. There is certainly a dmonths().

dmonths(1)

[1] "2629800s (~4.35 weeks)"

months(1)

[1] "1m 0d 0H 0M 0S"

Maybe dmonths() was added since the initial publication of this section? Whether it is makes sense to use is another question, and you cover that in the description. Perhaps it should ask, "What is the difference in output between months(1) and dmonths(1)? Is it logical to ever use dmonths()?" I'm sure someone will come up with a creative use!