Is it just me or does UA not show I inventory in expert mode? Do third party sites like Expertflyer and seats.aero show it?

Does this statement from wiki of this thread mean it’s better to book 4 people on separate PNRs to maximize available discount fare buckets?

“Going back to J8C5D3Z0P0, if you want 4 seats on a single PNR, you will have to purchase C fare, as there isn't enough inventory for D fare for everyone on the PNR and everyone on a common PNR must have the same fare class / fare basis.”