historical localities

Hi all,
We are beginning to georeference localities for the tri-trophic tcn and I am wondering what the present community standard is regarding notating the use of contemporary gazetteers for finding centroids of historical places. We all know the area considered a place has changed over time, and we are not generally using information from the year the insect was collected to acquire a centroid and error.
For us, we are adding in the georeferencing remarks if the gazetteer is contemporary or older. It seems this is something we will be filling out in the geo-remarks for every georeferenced locality (age of map resource).
Secondly, it would be helpful to have a list of resources somewhere for older gazetteers or maps online. Does anyone have such a resource? We are georeferenicng only North America.

Thanks!
katja