Not all EOS 1 Series cameras are EOS 1s.
The EOS 1 is a model of camera in the EOS 1 Series. It was the first in the series.
The 1N followed. Then the 1V. The 1N and 1V each had minor variations, such as 1N-RS or 1V-HS. A 1V-HS was simply a 1V sold with a high-speed motor drive already attached, while the 1N-RS was basically an EOS version of the special high-speed F-1 from the early '70s. Both the high-speed F-1 and the 1N-RS had pellicle mirrors, which allowed for their high frame rate. (Though the F-1 shot 14 FPS, while the 1N-RS shot 10 or so.)
So, the OP is not considering the 1V. Only the 1, the 1N, and the 3.
I haven't heard of the EOS 1S or EOS 1HS.