Manifold nibs were very hard, and later they had two breather holes and the slit in the nib became shorter.
Nibs for stenographers were very flexible enabling wide and narrow lines for shorthand, similar to a pencil which may produce different line width by changing pressure.
Later on, due to the writing habits of customers, for example their frequent use of ballpoint pens, nibs became harder giving a more uniform writing line with less variation.
Broad nibs in the 1960s were like today's Italic nibs and offered significant variation between the width of horizontal and vertical strokes.
The beveled or oblique nibs are intended for writers who hold the pen at an angle on the sheet. Oblique nibs have no influence on line width variations.
Since oblique nibs (OM / OB / OBB) are scratchy if held incorrectly and M or B nibs are generally easy writers compared to finer nibs, Pelikan in 2014 removed oblique nibs from their standard catalogue since demand was low.