I think is worth the effort --- especially if they are 'test' eggs --- to candle prior to setting and at Day 6 or shortly thereafter.
I started on 6/3 with a group of 40 shipped coturnix eggs and candling prior to setting showed 9 were cracked. 8 more candled clear on Day 6-ish.
If you don't candle, then you don't know.
Honestly, to me it has always been hard to tell on Button eggs anything more than whether they are clear or growing. But at least candling shows you that.