Are Diploma and Degree certificates with each having a different passing year valid?

As per your information provided, you have mentioned that you completed your graduation in 2016 and even your two-year diploma in 2017. This means that you have joined the diploma course while you were in your final year degree course.

As per a circular of the University Grants Commission (UGC) dated 28th December 2012, point no 1-b, a student can pursue a regular mode degree and also allowed to pursue a maximum of one certificate/diploma/advanced diploma/PG diploma program simultaneously in regular, distance or open mode. It means that your diploma in any form regular, distance or open mode completed along with your regular degree course stands valid provided it is done from a recognized institute or university. Kindly find the circular from the link: https://www.ugc.ac.in/pdfnews/0367166_morethanonedegree.pdf

For more clarification, you can also refer to the answers provided in the similar query post: Query regarding opting for two degree together

As per the latest norms of the University Grants Commission, a candidate can do a degree in regular mode and simultaneously he can do a diploma or certificate course simultaneously in distance/ regular/correspondence course. So as per your certificates, you joined in diploma while you are in your final degree and you completed your degree in 2016 and diploma in 2017. So there will not be any problem. Both your degree and diploma will be valid and you can apply for any posts you want without any doubt. All the best to you.

You need not worry for the year of passing of your two courses in two different consecutive years ie year of passing of your degree in the year 2016 followed by your diploma in the year 2017 showing a gap only of a year.
This indicates that while persuing your degree course during the second year of degree ( ie in the year 2015), you started your diploma course having its duration of two year. In that you passed out your diploma in the year 2017.
Now let us examine how far your degree and diploma are valid with the latest notification of UGC dated 28 th December 2012, which states while perusing a degree in the regular mode, one can take up a diploma/ certificate course simulteneously of either of modes ( regular or otherwise). Hence in your case there is no violation of the norm while persuing the two courses. You need not worry on that account.

As per the UGC guidelines two degree courses in regular mode are not allowed to be done simultaneously. For example one cannot do M.A. and B.Ed. simultaneously in regular mode. At the same time the UGC stipulation allows for one degree course and one diploma course in regular mode also. This is a special relaxation in the rules for diploma and certificate courses. In your case you have done one degree course and one diploma both in regular mode so as per the existing rules it is valid and fine. So you should not have any worry on this account.