1st picture - my seat pan. No lip for attaching canvas, has oval and square indentations.
2nd picture, what I would call a monroe seat, has shock absorber in front of the seat.
3rd picture, another style monroe seat? sock absorber behind the seat. Very different pan, much deeper and has pronounced leg indentations in front rather than being smooth.
4th picture, pan similar to mind, has oval and square indentations but also has a lip around the parameter.
5th picture, pipe style base, but a more shallow looking pan, this is advertised as an "early" seat used in '39 and '40
6th picture, Advertised as a '47 H seat, deeper pan with drain holes, leg impressions. Could it have been sold on an H or front an older model?
7th picture, pan similar to mine, no indentations