I have always thought that within means "till some point" while in means "at some point".
In 2 weeks - i.e. in 14 days from now.
Within 2 weeks - i.e. during today or the next 14 days, not later.
But what about "
within 100-200 days"?
I would say "from now and not later than in 100-200 days". But a native speaker told me that actually it means "from 101th to 200th day", i.e. not from now till the upper limit.
I would rather say "in 100-200 days" as I want to say "not sooner than in 100 days and not later than in 200 days".