In the absence of individual copper washers between each conductor there is a word for how the white wires are terminated. Let me think. Oh I remember now. That word is BOGUS!
By "feed through" I mean you can run power in say the top with one cable and out the bottom with another cable. A third cable likely means needing to double up conductors on at least some terminals - that is not acceptable with that type of terminal though it was done a lot.
The one switch that been individualized here has a center bus that would typically would pass the grounded conductor trough from top to bottom or bottom to top, the right side bus would pass through the ungrounded conductor, unswitched, and the one terminal on left side is switched output with other end of switch being the right side bus. In that setup one could bring two wire cable in and have three wire cable out that contains switched and unswitched leads and never double up any conductors on same terminal screw.
The OP image does have doubled up conductors on some terminals - that would be and should always been a NEC violation unless the device was rated for it - but like you said probably was not rated unless it would have provided some washers between each conductor or something of that nature.