At one time, it was just assumed that Top 40 wasn’t going to pass along much that Adult Contemporary radio could play, ever. For the first half of the ’00s, Top 40 was still in its “Terror Squad and Trapt” era of surprisingly aggressive hip-hop and active rock hits. AC found its currents in unlikely places, from Christian AC act Mercy Me’s “I Can Only Imagine” to “Live Like You Were Dying,” the song that finally made Tim McGraw a pop star.

But AC was doing fine without a lot of current music at that point. Top 40’s adult resurgence would take a few years to develop from its early beginnings with Kelly Clarkson and Gwen Stefani. Hot AC would need a few years beyond that for PPM ratings measurement to help it create stories. AC was the market-dominant format that could skim the top layers of 40 years of music, beginning with the mid-’70s and sometimes even earlier.

A decade later, very few ACs still hew to that format model. The last 10 years — basically, the years since Kelly Clarkson’s “Since U Been Gone” — have become central to the format. The format is now divided between those stations that combine those songs with a significant amount of ’80s gold and what has become known as “millennial ACs,” although most of those stations are more centered on the last 10 years, not the last 15.

The changes reflect the success of Mainstream Top 40 — its gains among women well into their 40s and even 50s, and its improved agenda-setting power for pop music. An AC that played its power songs 21 times a week in the mid-’00s was considered aggressive. Now “My 93.9” WLIT Chicago is in the 60s on powers, and other stations are more typically in the 40s.

There’s no reason that AC shouldn’t play more recent music. Many years ago, Mainstream AC’s conservatism was born of the oft-stated belief that “adults know what they like and like what they know.” The early-’80s ACs that played currents and differed from Top 40 mostly in texture were usurped by several waves of stations, gold-based ACs, then soft ACs like “106.7 Lite-FM” WLTW New York that played no currents. But the influence of CHR and the “power of now” that pervades pop culture and transcends format means that adults both know and like the hits sooner.

None of this has put AC radio back in the business of breaking currents. CHR re-established itself as a valid supplier of music around the time of Clarkson, Pink, and Lady Gaga, and AC has happily followed its lead. Sometimes, Mainstream AC has ended up in some unlikely places as a result. Did “Chandelier” and “Boom Clap” sound right at the format?  They’re just the updated version of Gaga, right? Or were they too noisy and aggressive for the format? But if your gauge is “anything liked by adult women,” CHR can reliably create music that adult women like.

Even singer/songwriter pop starts elsewhere. A decade ago, WLTW PD Jim Ryan propelled both Daniel Powter’s “Bad Day” and James Blunt’s “You’re Beautiful” from the European charts. These days, such songs flaunt their singer-songwriter credentials to go to Triple-A first. James Bay’s “Let It Go” took a year to get from Triple-A (in late 2014) to AC and Adult Top 40, (which was still four months ahead of CHR). Passenger’s “Let Her Go,” a similar worldwide smash to the Blunt and Powter hits, needed three months to get from Hot AC to AC (with Triple-A in between). It hit the AC chart just a week ahead of CHR.

This arrangement has been fine with everybody for a few years now. And yet …

CHR Does Not Have AC’s Best Interests in Mind. It’s not supposed to. CHR hits such as Justin Timberlake’s “Can’t Stop the Feeling” that are obviously appropriate for AC immediately are the exceptions. So are songs such as Shawn Mendes’ “Stitches” that become surprise AC smashes. But Top 40 is still a format that runs on audacity, and it’s healthiest when there’s a “Work From Home” that will take a while to sound like a Mainstream AC song, if ever. Right now, CHR has a surplus of noisy, dense midtempo records that may make it to AC eventually — just by establishing an adult female quorum — but will be sonic judgment calls for a while for most AC programmers.

Anything Can Make The AC Chart, But For Real, Though? As AC finds its footing in 2016, some AC stations continue to push the format boundaries that a way that appears successful, but then evolve to Hot AC. There have also been a handful of stations that confound the airplay chart world, such as WDVD Detroit and WPLJ New York, that are Hot AC in texture but more conservative in timing. So when you see that “I Took a Pill in Ibiza” is a top 25 mainstream AC record, it’s hard for AC PDs to know whether it’s due to stations that will be reclassified in a week.

AC Is Not One of CHR’s Dominant Styles. Singer-songwriter ballads take so long to get to mainstream top 40 because almost anything pop/rock takes nine months or longer to get to top 40. “Let It Go” waits in the same pile with much different Alternative crossovers and has to find its slot in between the last and current Twenty One Pilots singles. Even if it’s only a few records a year, AC is being deprived of at least a programming weapon or two. Adults like some of their kids’ music, and we’re all happier for it as an industry. But that’s not all they like. CHR isn’t necessarily giving 16-year-olds everything they like, for that matter.

“Let It Go” Doesn’t Need a Year. James Bay sounded like an AC record right away. It just took a year to get the format’s attention, even with an appropriately aggressive label push. And then one wonders, would the adult women listening to the format now not have liked it without lateral radio support elsewhere? Do we really need the artifice of breaking an AC record somewhere other than AC first? More than a decade ago, starting a record at AC became more of a stigma than a story — the sign of a veteran artist who couldn’t get airplay elsewhere. But must it be that now?

More Places To Start Hits = More Hits + More Careers. CHR has benefited from creating its own hits, but not necessarily from fewer hits starting elsewhere. If AC started AC records, and we destigmatized those stories within the industry, there would be more hits for everybody, including Hot AC and CHR. There would also be more sustainable artists. New singer-songwriters are coming along at a rapid clip, which tends to commoditize even a “quality” artist. CHR acknowledges those artists, sometimes quickly, and gives little thought to what comes next for Vance Joy or Hozier. Again, it’s not its job.

We’re talking about a relative handful of songs here — almost certainly not enough to radically change the Mainstream AC template. But even for those stations playing five to nine currents, there might be better choices. And there might be ways to better reach those listeners who aren’t willing to do the work of trying to find the handful of potential pop hits they might like at Triple-A.