Work and Mobile numbers are separate in contacts. Yet texts seem to be under the same thread, and no way to know which number it goes to

So the contacts allow you to add a Work and Mobile number for one person. Yet when you text either it goes under one single thread and it doesn’t seem like there’s any way of knowing which number you texted, since both are under the one text thread. Any way to distinguish? Or how to know here?

Thanks in advance!