Assuming DH hasn’t had the personal/vanilla Platinum yet, have you thought about supporting him from your Biz Plat link? The Biz Plat has a 20k MR support bonus that would go to your account. If you open the support link in incognito mode, you can click around to the vanilla Plat for DH to apply, and it might pull up the 75k MR incognito offer (some people report seeing a 70k MR offer; the 60k MR offer is the same as the public offer but you’d get the 20k MR support bonus in addition) (and try different browsers, and/or servers if you have a VPN if the higher offers don’t come up). That’s about as close to the 100k MR offer as you can get without finding the Platicorn.
Remember that MR cards max out in support clicks at 55k MR, per card, per calendar year. So for the Biz Plat, that’s just two clicks at the full 20k MR, and one 15k MR click. (The BGR/Biz Gold also has support clicks worth 20k MR, capped at 55k MR per year.) Just be sure of how many support points you’ve already earned on the card this year before using it to support again.
I actually double checked with Amex chat today on previous cards for both DH and me. I was right in my recollection--he's never had a personal Amex card. That makes his pop up on the 100k Schwab offer even more of a head scratcher. The only thing I can think is that we have a big charge ($10k) on his Amex business blue card that went in right after the last statement. The statement for that hasn't hit yet so I'm going to try on the Schwab again after we pay that bill. He puts tons of regular spend on the Business blue, and the only other card on his
Amex record was the Starwood business that he had for a year and rarely used. He closed it once the first statement hit. He would have used it more it they hadn't changed the points earned with the merger. But if the Starwood is the problem, he got the pop up on a personal card for a business card that he cancelled last April. Again, with tons of regular spend on his only current Amex card. Weird!
If the Schwab attempt fails again after paying the bill, then I will definitely try the personal platinum through a referral link from me. I've never done the incognito route so hopefully I can figure that out. If he still gets a pop up, I'm going to be pissed, LOL.
I have had the personal platinum before (closed 2015), which probably explains why I wasn't eligible for the Schwab 100k. Strangely on my Amex website card offers it has the platinum 60k offer in there for cards that I'm allegedly "prequalified" for. I assume I'd get the pop up if I tried though. If DH can't get through the pop-ups for a personal, I may give it a try though.
I went ahead and cross-referred both of us for our CIP#2s today. Both of us got the pending/need more consideration message.

I was hoping to sneak through there since we haven't had Chase cards in a while, but I guess not. I'll wait a couple days and check the status number.
So I think my next move is to try the Schwab again once the bill is paid. If that doesn't work, I'll try to refer him from my card and pull up the 60-75k personal offer. If that doesn't work, I'll have him go for the business version via the phone call and I'll go for the "prequalified" personal. I love my MRs, but they do make it a PITA. We fly British Air a ton so I am going to look into the Chase BA card upgrade for a credit toward the ridiculous fees after the CIP application process is finished (+30).