When looking for Lamy 14ct nib prices I've found there are 4 different Lamy reference numbers: Z 55, Z 56, Z 57 and Z 58. Apart from the fact that the Z 57 is black, the other main difference I can see is that the Z 55 is the only one with a breather hole.

In steel nibs Lamy Joy nibs: 1.1mm, 1.5mm and 1.9mm also seem to come without breather holes compared with the standard Z 50 nibs for Safari, Nexx, Al-Star etc.

Has anyone ever found any difference between the writing performance of the Z 55 and Z 50 nibs with breather holes compared with the others that don't have them?

I haven't noticed any significant writing difference when I swap a standard Z 50 EF, F, M or B with breather hole to a 1.1 or 1.5 without and can't help but wonder why Lamy make some with and without.

People do tend to swap nibs like these between Lamy models that they all fit and I wonder if maybe breather hole nibs are designated only for use in those pen models that they originally start life with or vice versa. Or is the absence of a breather hole just for cosmetic appearance in some of their models? Exactly what function does the breather hole perform if it is unnecessary in some models?