Sure, Alexey. I was just comparing with the 1b which had previously the same modification, concerning the left corner. And I am not confused!

So, there were (at least)four alterations around the 54/64xxx serial numbers:
- the corner around the speed dial, from round to angled (passage 1b/1c). We knew it, of course,
- the left corner, modified between the 59349 (my camera) and the 65414 (the one you show), well known too, even if we find later rare covers with the early shape,
- the vulcanite (it's another matter),
- this famous second pit I had not noticed. I confirm: it exists too on my early 1c s/n 59349 and my other 1c before. And thanks to have seen that!
Certainly the stamping tools were changed to obtain the modified left corner and the second pit.
Amitiés. Jacques.