Excellent work on adding postcodes https://osm.mathmos.net/addresses/pc-stats/DE/ 

DE55 Alfreton had previously only had a few postcodes added from Amber Valley Food Standards and for existing objects from Code-Point Open centroids so is now much improved

If possible please add addr:city for the relevant post town Alfreton, Ashbourne, Burton-on-Trent, Derby, Matlock, Ripley, Bakewell, Ilkeston, Swadlincote and Belper only https://osm.mathmos.net/addresses/post-towns/DE.html for DE postcodes

Sometimes useful to add addr:suburb, addr:village or addr:town https://osm.mathmos.net/addresses/addr-tags.html although I have only ever used addr:town for Wirksworth (DE4 addr:city = Matlock) and Castle Donington (DE74 addr:city = Derby)

I would not normally add postcodes for non-geographical (PO Boxes etc.) postcodes like https://www.openstreetmap.org/node/12335209625 flagged as “Multiple Units at the same location (ML)” and excluded from the statistics https://osm.mathmos.net/addresses/pc-stats/DE/DE55/4/ but is probably harmless to do so


