Hello Rishabh,

Let me make you more clear from an example,

Suppose you have completed your class 12th from CBSE board from PCM background and then you have completed your B.Tech course as well on the basis of that class 12th marksheet but now if you want to improve your marks of class 12th and also want to add Biology in your background then you can appear for PCMB exam through NIOS and in that case your both degrees will be valid and you can use the degree whichever has good performance.

I hope your doubt is cleared now, if not then feel free to ask in comment section.

Good Luck!!