hi friend,
the best case is having full information before doing synthesis, but real work is not like that.
in my case about multicycle path, almost customers did not give me full specify about design for synthesis. and I had to do synthesis without this info, then if STA result after synthesizing show violations, I review and feedback to customer for some special paths.
I think the work also the same if you have these specifications or not, it's rarely to pass all timing at the first time I run synthesis - I mean rarely we have "super-full"/perfect design's specification for synthesis. we need to work together with Designers.