Well, in the past if I had to update an xref and the new version had a different insbase variable than the first, I'd open the old drawing and draw a line from (getvar 'insbase), then snap the end point to a point on the house that is the same as on the new version. Then I'd copy the line using copybase and select the endpoint of the line (the part connected to the house. Then I'd paste the line into the new drawing using on the same point I copied it from. Finally, I could either set the insbase variable to the startpoint of the pasted line. This will set your xref in correctly.