There are two different groove widths and the difference isn't very much but try cutting composite cork to get a too wide one to fit and then you can see why they provide both widths. They need to fit tight in the groove so only one is needed.
This is a seal for the rear main bearing with slinger removed. Not the bearing housing to oil pan cork
Just tried installing a 1 piece rear main cork seal and it was too tight to fit into the groove. Will let the cork soak in oil overnight and try again tomorrow.
Good luck w/that, it's been my experience that when cork is soaked in a liquid it expands, .YMMV