Have to agree with this bit. A derby is between two clubs in the same city, not big local games hyped up by Sky since the 1990's. Sunderland vs Newcastle, Derby vs Forest, Leciester vs Coventry, Swansea vs Cardiff, etc - not derbies.
It is though - not many folk clearly fancy sitting below United fans. If the West Stand Lower could accommodate 2,300 Blades, we'd sell out the top tier for this game, no bother.