since the difficulty level of each shift is different so how does NTA decide 1 cut off mark for all shifts for a given category

Hello,

That's why nta choosed the normalization process for evaluation.  The normalization through percentile is done in jee exam.

Nta defines normalization as "The process of Normalization is an established practice for comparing candidate scores across multi session papers and is similar to those being adopted in other large educational selection tests conducted in India. Fornormalization across sections, NTA shall use the percentile equivalent "

the percentile for each session are calculated then these percentile are merged to prepare an overall ranking list. Which is called overall ranking.

Hope you understood the ranking and scoring method easily.