These credenzas have been floating around NYC for decades and its always been a bit of a mystery as to who designed and manufactured them. Often they are sold and attributed to Florence Knoll which is totally understandable as they are virtually identical to her iconic 1960 credenza that I think was first used in Saarinens's CBS building. These credenzas are never signed, the tops are a tiny bit thicker than the Knoll ones and the metal base is constructed differently. Everything else is the same. I've gone through piles of design books from the 60's pertaining to mid century office furniture and here is what have come up with.
These credenzas almost aways have some sort of connection to Skidmore Owings and Merrill buildings. Many of them have Chase tags still in them. The Chase buildings were such massive projects ( the tower downtown was the biggest in the world at the time ) that I think office furniture was custom made for them. The person in charge of interior design for many of these projects was Davis Allen. Allen was one of the main figures within Florence Knoll's Knoll Planning Unit throughout the 1950's. He was surely present and involved in parts of the design process that gave birth to the credenzas that would be a staple within the Knoll catalog for years to come. By the 60's Allen's affiliation had switched from Knoll to SOM as their in house interior designer and the projects for Chase were some of the most ambitious of his career.
It seems odd that Allen and SOM would blatantly copy the work of his old boss at Knoll. It seems more likely that the Chase jobs were so big and required such a large quantity of product, that a custom credenza was created for the job and manufactured separately from the almost identical Knoll pieces. I can't imagine that Florence Knoll was not aware of these pieces and that she did not give Allen and SOM her blessing to manufacture these them.
This of course is all one big educated guess on my part. I could be wrong but until there is information out there stating something else, this is my story and Im sticking to it. Normally I am pretty strict about only have Knoll and Herman Miller stuff in the shop, but Ill make an exception for these. They have enough of a connection to Knoll and Im always interested in anything relating to SOM.