When adopting the compendial method impurity profile of your drug substance should same as that of USP method. If it different then full validation is required and if it is same it is upto you at what extend verification is to be done but impurity spiking and its recovery is must.

You better at least try to do method transfer and see whether you can meet the USP specifications.  If not, the full method validation should be done as the drug substance may be novel.

But Mr. Udaya same API can be synthesized with two different route where impurity profile will be different hence compendial method cannnot be used as it is published method who has filed to FDA with only one route and not considered another route.