"Limit test" vs. "Titration" in a pharmaceutical guide
From what I know, rules for making a monograph are not about giving an exhaustive list of all the analyses possible. Guides describe international agreements about what is recommended and sufficient to identify a substance and its impurities.

A titration is considerably more tedious to perform and validate (see ICH Guideline). If you use titration in a monograph, people referring to it will also have to use this method. Unless you also included a limit test but, if you did so, why bothering carrying out titration? Overall, you would waste your time and, most importantly, others' time.

So the sentence "limit test should be used..." should be read "we agreed that a limit test gives enough information in this context and we prefer it over titration".

HTH