No, many a times you might be able to secure a seat in later rounds of JOSAA, while you dont get any seat in Mock Rounds, or perhaps you have not given many options. You should Ideally fill options with Previous cutoffs in then Range ( Your Rank +/- 5000), in the proper order of preference.

My suggestion would be before locking the choices, do revisit them and revise the order of preference on basis of previous years cutoffs, from highest to lowest . All the Best.

For more information on cutoffs and college prediction do follow the links below

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

https://engineering.careers360.com/jee-advanced-college-predictor?icn=QnA&ici=qna_answer