I found it! Finally figured out why IS says PD images must be from before 1885 (and yes I know they are in Canada, I looked at the Canadian laws too and they are less restrictive on old works than the US laws, but they make their own rules?)
Type of Work - Copyright Term - What was in the public domain in the U.S. as of 1 January 2013
Unpublished works Never Published, Never Registered Works
1) Life of the author + 70 years
2) Works from authors who died before 1943
3) Unpublished anonymous and pseudonymous works, and works made for hire (corporate authorship) = 120 years from date of creation
or
4) Unpublished works when the death date of the author is not known = 120 years from date of creation
Works created before 1893Works Registered or First Published in the U.S.Date of Publication -
Before 1923 = None. In the public domain due to copyright expiration
1923 through 1977 -
Published without a copyright notice = None
1923 through 1963 - Published with notice but copyright was not renewed = None. In the public domain due to copyright expiration
1923 through 1963 - Published with notice and the copyright
was renewed - 95 years after publication date
-=-=-
In other words, 1924 works will first move into the public domain in 2019. 1923 works had already passed into public domain when the law was written, so they remained with that status. You can't go back and copyright something, once it's public domain. Which applies to all dates and works. Once they go into the public domain, they are ALWAYS and forever in the public domain.
There are traps and complications, say a book is Copyright 1922 and the printing is 1933, it's protected from the later date, as a new version.
But the whole point of all of this was to discover why iStock had refused a work from 1899, they assume the author of the artwork is unknown, until I can provide facts to show otherwise. If a drawing has no provenance, they assume it's anonymous.
"==> Engravings and illustrated reproduction scans must be dated from 1884 or older in order to be acceptable.
This file includes content that may be subject to copyright or trademark protection. Certain use of this file creates risk of copyright/trademark infringement and we regret that it cannot be accepted, unless this content is removed from the file."OK then, I'm happy to have discovered some law and reasoning. While the dates aren't a perfect match, at least I understand the cut-off point and have a reasonable reason why it is the way it is. (unlike the response that I got which said, "contact Scout") No reason to bug Scout review when the problem is something from legal.
Some day maybe I'll meet a Canadian lawyer who can explain the fine points.