quite frankly you aren't gonna get a lot if you are only gonna post with the author's permission. and I don't see why they would care if you linked their fic without them giving an okay first. it is literally just promotion for them.
I know what you're saying anon, I understand completely where you're coming from, but I have my own reasons for asking author permission. I'm planning on personally asking around tomorrow evening when things calm down in my household and doing it manually. I only ask for author permission because I want to make sure the fic is from the person themselves and not someone posing as someone else, if that makes sense. I don't believe anyone in this community would try and do that, but I've seen it happen multiple times to people I know and have had it happen a few times myself in other communities.
Ideally, I'm trying to look out for the writers since on the internet it's so easy to steal from people and pretend to be somebody you're not since there aren't hard copies of things. Even with the author's page, for example, there are people who use pen names on fic posting sites (such as myself) that don't match up with their tumblr urls, so I might miss some people if neither correlate when posting and linking the community together, and I feel it seems rude of me to go and leave a comment on an author's story (whether I've had the time to actually read it or not because life is very busy for me right now) asking if they wouldn't mind their story being linked since, to my knowledge, ao3 doesn't have an actual message system like ff.net does. I only really want to make sure both parties are happy with their stuff being linked other places and that I get all the links correlated together ^^
I hope that answer suffices, I feel I rambled a bit in certain areas, and that it clears up why I want author permission before archiving ^^
