Remember that some families kept in contact more than others for a variety of reasons. Your great-great-great-grandfather in 1850 may have had a rough idea of at least the county where his siblings were living and might have been able to at least write a letter to them with that address and have them get it. Other ancestors might have had no idea where their siblings were located or any way to contact them.
It can vary from one family to another and one place to see evidence of it is in estate settlements or probate records. A Civil War pension for one ancestor indicates she knew where her scattered siblings were. Another indicates she had no real clue where her siblings were located.
Of course, that may also be because they might have provided testimony inconsistent with hers.
But not every family maintained the same level of contact. Don't assume that they did.