Not quite sure what you mean with "the metadata crawlers" and what software you have used so far. But if you use MusicBrainz Picard it will load and store the original release date in a special tag. Many players however do not support this tag, in this case you can script Picard to write the original date tag to the normal date tag by adding this script to Options > Advanced > Scripting:
Picard is not really the best tool for just changing a single tag, it is really meant to pull data from MusicBrainz. But if you want to do it you can set all tags you don't want Picard to overwrite in Options > tags > Preserve theses tags from being cleared or overwritten... . You can find a list of tags in http://picard.musicbrainz.org/docs/tags/
I would strongly suggest to keep the MusicBrainz ID tags, though, as it allows you to easily retag your files again without doing all the matching again.