I think this is totally fine. I'm on the exact same situation (student, then work permit, then PR).
On the physical calculator I also only put student from 2015 - even though I was a student for few years before that - as it was clearly bolded and specified that they only wanted the info from 2015 to 2020.
On the actual application form, I put 2013 (rather than 2015) to match when the study permit was issued. So if anything, I have a mismatch there which isn't ideal, but I truly genuinely believe you're fine as they do indeed only care/look for the 5 year eligibility period