They don't even show up as an option. I can use new mods fine in Worthy armor. I didn't notice until I was fiddling with an older chest piece and a new mod was available that I hadn't noticed earning. It's consistent across all my Arrival armor and all three of my characters: according to my Holdfast armor, there are no new mods. EDIT: I just checked my Collections to get a list of my specific Arrival mods (I've got Argent Ordnance, Lucent Blade, & Kindling The Flame, to name a few), and discovered that they also don't appear in my mods collections! I can equip and use any of the general Arrival mods on last season's armor. If I want to level up, though, my options are burning through Upgrade Modules or skipping all the new mods. EDIT: I'm not the brightest. Thanks, @Xaren, for reading my own screen to me. :P