On older installations of Hardieplank lap siding the field/butt joints would have an “appropriate gap”, which at one time was specifically designated as 1/8th of an inch, and the gap would (typically) be caulked (very few exceptions applied). Since they were caulked, this created a maintenance issue: they had to be kept caulked. More recent installations, especially after 2008, will have flashing used at the field/butt joints, not caulking, which is now the “preferred” manner of installation by the manufacturer, though at the time of writing the installer could still use caulking as it will not void the manufacturer’s warranty, per their own information. Another thing that changed was face nailing at the field joints: this lead to cracked siding at the lower corners by the field/butt joints. They are now blind nailed (meaning that you can’t see the nails).