Hello, 

To get admission into any college affiliated to Mumbai University for the academic year 2019-2020, you have to appear for the qualifying exam of 2019. In this case, you'll only be eligible to apply for a course with Mumbai University if you have taken MHT CET 2019. You can also apply to colleges using your JEE Mains 2019 scores. So, unfortunately, you will not be able to secure admission on the basis of MHT CET 2018 scores.

Maharashtra Common Entrance Test is conducted every year for admission in undergraduate courses in different colleges of Maharashtra.

It means that every year fresh score is required for admission. Its validity is one year only in which it is conducted.