S&P Global Market Intelligence has released a report showing that office remains a tale of two markets.

The gap between Class A on one side, as well as Class B and Class C on the other, has only increased over time. The most noteworthy sign is that tenants consider the state of a landlord's balance sheet and willingness to invest capital in building improvements. The former exhibits worry that a landlord is a going concern, which is also an important consideration for lenders. The latter is a statement of wanting a "good" office property to remain so.

But it's important to remember what Class A represents, as there aren't hard-and-fast definitions. Early this year, Cushman & Wakefield estimated that the top part of the market comprised 10% to 15% of total office inventory. That raises the question of what percentage of bank office loan portfolios might be in real trouble. It's mathematically unlikely that all banks have largely lent to overwhelmingly top-quality stock.