AMAZING WORLD OF DC COMICS ran a sporadic 17 issues, and had 2 to 3 months of previews per issue.
(August 1974-April 1978)
https://www.mycomicshop.com/search?TID=463981

Oddly, I can't find any image or info on the DIRECT CURRENTS newsletter in the ad above,
but it is said to have been published for about a year.

DC COMING ATTRACTIONS, an 8 X 11" 4-page monthly newsletter, replaced it from July 1978-1984
https://kupps.malibulist.com/2015/12/01/obscurities-dc-coming-attractions/

The DC RELEASES newsletter of monthly titles, also 8 X 11", ran from 1984-1988
https://www.mycomicshop.com/search?TID=13379021

DC DIRECT CURRENTS, a 7 X 10" full color comic size previews flier, ran from 1988-1996.
https://www.mycomicshop.com/search?TID=512681
https://www.mycomicshop.com/search?TID=13168231

DC COMING COMICS, a 1992 aborted 4-issue promotion attempt
https://www.mycomicshop.com/search?TID=19643285


I remember in the days of the DC message boards (2000-2003), they previewed monthly comics
online on DC's site, and I used to read through them. I don't know at what point they
discontinued the printed version.
I think it's a mistake not to have a page in each issue listing all your monthly releases, whether
DC, Marvel, Dark Horse, Image, or whoever. Where better to promote your line, than in the
comics themselves? As is obvious, I love a lot of these ads from the 1960's/1970's era, where
they had the good sense to do so.