Old comments are flagged as new.

Old comments from months and years ago are flagged as new.

I think they are only flagged as "new" when they are new to you.  I noticed that when I opened this one and then closed it, the "new" flag disappeared.
 

Yes, I think Bikeophile is correct. 

I've been enjoying going through the old comments and often discover useful insight or good links to other resources. 

Danke Schon.