That's the way it is - unfortunately. Posts vanish after some days. If you look for posts older than a week you have to search for them with the search engine you usually use or use Esteem.
I do some curating, too, and know how much work it is to separate the wheat from the chaff. I mosly use the Steem Search Engine. It's ugly and the way it refreshes automatically makes me want to pull my hair out but you can look for posts in specific topics with low rewards but more than just a photo and a dozen words... Another tool I like for searching is Custom Feed - looks better and has some nice features, too.
And yes, there are four to five tags where I use "/created/" daily. It's the best way to stay up-to-date in my niches of interest without cluttering my feed with a lot of posts I don't want to read only because every now and then someone writes about the things I'm interested in.
The first two work like a dream. Custom feed wasn't showing me all the recent results in my tag search, just 3 month old posts and beyond.
Thank you for sharing, those are all very useful. Esteem is pretty good for a cleaner design. Steem Search Engine would be great for filtering through lots of posts for quality stuff, or for help finding a post I can no longer locate.