Long shot, I know. But if you ever decide to sell just the collar I would be interested. I only have the black.
And I think you should keep this one.
The collars from my J23 and J 24 are not interchangeable, the snaps are all at slightly different places, a collar needs to be matched to a specific jacket.
As @oneterrifichog said Stuart asks that you send the jacket or collar back when ordering a new collar so he can make sure the new one fits.