The mela-janya relationship between ragas has been in existence for a long time. However in the last 100-150 years there has been a shift in the nature of this relationship. Increasingly we have moved to a purely swara based classification of a janya under its parent mela. The modern ground rule has been to include a raga as the janya of the first mela that carries all its swaras. This rule goes against a much earlier method of classifcation which used the raga's melodic and aesthetic structure to determine its parent.
The need to write a lot about the music especially in a global scenario where things are expected to be spelt out in more detail before being actually experienced is one of the reasons for the popularity of the mela-janya system among musicians and music lovers. My guru was of the firm opinion that the mela-janya system itself is irrelevant to performing musician and it serves only academicians. For instance how much does the study of phonetics help in our communication skills. In today's context when communicating with others we hardly employ the theories of language. Similarly the grammar for a system of carnatic music may have evolved into a complex structure but it should not come in the way of performance or experience.
In my own experience I have often encountered the question from rasikas when faced with a fairly uncommon raga - Which janyam is that raga? This is often like asking what the ingredients are of a new dish that we eat! Practically however there is a paradox in this question. For instance lay listeners often identify a raga with something that they have heard in th past. So some parts of mukhari may sound like bhairavi. Especially when they hear a more uncommon raga like Narayanagowla - "Does it sound like Kedaragowla a bit?" is a common doubt. This is actually uderstandable. But when someone wants to what janyam the ragam is then there is a clear case of not understanding musically but demanding pure academic information. Here is my argument - The modern mela-janya relationship is based on swarams. So if Senchu kambhoji is a janyam of Harikambhoji then it means it carries the same notes of HK, but with a different musical structure in its scale, not because it sounds like Harikambhoji. If one wants to know this with a view to understanding the musical notes of the raga then one should be able to differentiate between the suddha and the chatusruti dhaivatam when actually sung. So if one can understand that difference, one can also know which notes occur in the raga being sung. It is then a question of basically applying those swaras to the mela scheme to derive the parent raga. The problem comes when I sing Shamalangi in a concert and a rasika asks me "Which janyam is that ragam?" Classic Catch-22!