I don’t know which wiki pages you are looking at, but I’m working from http://wiki.openstreetmap.org/wiki/Proposed_features/House_numbers/Karlsruhe_Schema, which definately does not add the interpolation way to the relation. Since the interpolation way was designed to be a temporary construct, until all houses on the stretch of road it covers have been entered individually, it has no place in the associatedStreet relation. Only the nodes have to be added as members, in addition to the (section of) street to associate those nodes with.

I’ve stuck with the addr:street tagging on the nodes, since it’s much faster to enter. But if I did associatedStreet relations, I would probably do this:

  • Create interpolation way with 2 nodes. Tag it, and tag the two nodes with addr:housenumber.
  • If necessary, create any interim nodes into the interpolation way while creating it, or after it’s been created, and any individual nodes outside of the interpolation way, but still for that stretch of road. The latter is commonly needed when you start off with numbers like 1a, since those cannot be on the end nodes of the interpolation way.
  • Create associatedStreet relation, add the nodes and the associated street as members.

Using the plugin, you’d have to account for 2 scenarios.

  1. You create an interpolation way with 2 tagged nodes, and create the relation with that. That’s what you’re currently doing.
  2. After that’s done, extra nodes are created in the interpolation way and tagged accordingly, or individual nodes are created that have to be in the relation as well. Select those nodes, and the street to associate them with, and invoke the plugin again. The plugin then recognizes that the relation already exists, and only adds those selected nodes to the relation.