Part of it is the fragmented nature of rumours and which bits of the process people have seen and when they know about it. GW switched about a year from little additions to ranges to renewing ranges, which means the pipeline behind that switched about 3-4 years ago. Rumours get spawned from concept art, not all of which is used, and there can be big differences between the art and the finished minis, test sculpts and prints (again not all of which are used, and I was expecting the Eldar Spirit Seer to come out ages ago, but the model got forgotten about when studio guys got moved around and it sat on someone's desk for 3 years) or when it finally gets to the design studio and they have to work out what the hell to do with the pile of models they've just been given, and then comes playtesting, box art, manufacturing, etc. Leaks trickle out from various points and get mixed in with channers making stuff up to wind people up. And then you get a bunch of chinese whispers or potato cam shots.
I heard some squats rumours a couple of years before Kharadron Overlords, and discounted them because a) Squats and b) people keep seeing unreleased/limited release stuff from 2nd ed in peoples collections and getting excited.
I got told about baby stealers being a big deal in the new GSC, but it turns out it's just a bunch of character models getting little buddies and there was a lot of chatter because genestealer familiars are as popular with the sculptors as Nurglings are. Similarly GW have only shown 25% ish of the new Chaos stuff and Blackstone was a soft preview of the range.
Warcry I've known as Killteam but Aos since autumn last year, but I've not known the details regarding it as a) I'm not interested in AoS much, though 2.0 softened me a bit and I've played a bunch of Underworlds and think it's one of the best designed GW games in years and b) I was far more interested in the stuff coming out for KT and 40k. And 40k is going to hit us like a train this year.
However Darkoath (which will include the StD range) has peaked my interest, as sixpack barbarians done with modern sculpting hit's the spot for me as an old fantasy player. I will definitely be getting into AoS Killteam.
I was expecting Warcry at the back end of this year, and the LVO announcement to feature more of the Chaos stuff or maybe hints from the big 40k summer releases, but it's possible it's coming sooner.
I've been told the leak seen is pretty much correct. Watching the trailer though you can pretty much educated guess half the background detail, and Stormcast vs Chaos is also a pretty easy guess from there.
I know the Kill Team studio guys were pushing hard to get new minis assigned to them (and used the slow sales on the faction starters and commander sets to say that they needed something new) and now they've got the new format we've seen in the latest release of a more aggressively priced product with new models and more material (twice the missions per set for example). I had hoped they'd follow the new coke formula with Warcry, and will be disappointed if they don't.
And Kill Team: Inquisition around Easter (though with White Dwarf losing the new release section the schedule is even more malleable now). Wade was incredibly pissed I a) knew about it and b) had mentioned it in public but to be honest I completely lose track of what Community have talked about, as I was sure they'd shown a bunch of stuff they haven't and I'm being a bit more circumspect now.
But this month and next month features the last two Underworlds boxes for this season, Vigilus 2, a range refresh for Chaos in 40k with a giant pile of kits, Primaris Wave 2, one or two more AoS battletomes, possibly another Kill Team wave and then KT:Inquisition at the back with some Specialist stuff sprinkled in as well and that's just the next 6-8 weeks.
There's a lot of 40k this year, a lot, and the release schedule is not slowing down with at least one big £95 ish box a month every month for one system or other, constantly slamming into our wallets.