Previously developed land

We have a large piece of land which was formerly single family detached housing. We are redeveloping the site, and it is clear that all of the single family lots, and roads are previously developed. We are however incorporating a small remnant piece of land which was owned by the town, and was part of the road right of way. The were no property lines delineating the parcel from the adjacent rights of way. Although as far as we can tell there was no actual construction on this piece of land, we don't think it should be classified as vacant or not-previously developed as it was part of the right-of way and had been maintained by the town as part of the road. It doesn't impact our classification of the site as infill, but it causes a problem for GIBc7 as this part of the site is not previously developed and we would be required to preserve a small (20% of this piece of land is about 6,600 sf) as undisturbed. Thanks for any clarification. Tyler