Scratchy nibs are mostly misaligned nibs............with your loupe see which is the up nib, with your thumbnail, from the breather hole press down so the up tine is under the lower tine...hold for 2 to three seconds, check, try it again, it might take 3-4 tries.
That usually cures scratchy. I've had no scratchy Geha nibs.
The other part of scratchy is often holding a fountain pen like a ball point before the big knuckle...with your pens, not a problem for you.....could be for others....newer to fountain pens.
I have had drag on many old sat in the dark of the drawer for a couple of generations, caused by 'iridium' micro-corrosion......'iridium rust'.
Back in my cheaper days I used a good quality brown paper bag for that.....but most don't know about bag quality any more..........so use only the smooth side of the buff stick....and not a lot is needed. One is not 'grinding' nor making butter smooth.....just removing the drag to get it up to 'good and smooth' the level under butter smooth.
To confuse things even more with 'softer' nibs of the era.....There are semi-flex and maxi-semi-flex nibs that outside of Osmia are not marked.
I chased MB slowly....in they are expensive, and checked the nibs in the live auction. I had and still have a nice semi-flex KOB, one a rolled gold 742 exactly between semi&maxi...the only one I have...27 semi\s &16 maxi's....and a nice maxi on a very well balanced medium small 146.
Not counting my superflex 100n, I have three early 50's Pelikan maxi's. An Ibis, 500&400NN OF on a Pelikan to 5 semi-flex Pelikans. Three of my Geha 790/760's are semi-flex....one is a Maxi...and my 725 is semi-flex....such a different nib, I'd never expect a maxi....
So outside of Osmia, a maxi is luck of the draw. Osmia's steel nibs are as good as their grand gold nibs...so don't be a fool gold snob, like I was and avoid Geha or Osmia steel nibs.
Everyone says poor Mozart dead at only 36. None say poor Mendelson, dead at only 38. His family only allowed him to start at 20, but before, musicians use to come to the Mendelson garden to steal the music of Mendelson and his sister. A good artist also.
www.nibs.com/blog/nibster-writes/nibs-germany Info on Bock nibs
The cheapest lessons are from those who learned expensive lessons. Ignorance is best for learning expensive lessons.