Yes, I’d like to interpolate just the unit numbers. The situation is exactly like your example, except that all apartments share the same street address. They are arranged in multiple buildings as follows:

Building 1: units 100-108
Building 2: units 200-208
Building 3: units 300-306
Building 4: units 400-408
And so on. Not all buildings have the same number of units, but this should be handled by interpolation (should, but isn’t).

What I would like to do is use “addr:unit=100-108” and have any search within that range (575 Shelton Mill Rd Apt 101, for example) to return building 1 within the complex. Otherwise, I think interpolation lines should handle unit interpolation exactly the same way they handle house number interpolation. Currently, they do not recognize unit numbers applied to their end nodes. As a result, the only way to return results for a search for a specific apartment is to add a node for each apartment and address each node individually.