Occasionally - rarely - a Nominatim search will return a hit with a key "address29" or "address26". There is no mention of such a key in osm, and I can't find any explanation in Nominatim.
Here's an example. Search nominatim for bamako (the capital city of Mali). Among others you'll see:
{"place_id":"104544188","licence":"Data © OpenStreetMap contributors, ODbL 1.0. http://www.openstreetmap.org/copyright",
"osm_type":"way","osm_id":"197528638","boundingbox":["47.4519905","47.4523668","-0.5565341","-0.5561207"],"lat":"47.4519905","lon":"-0.5565341",
"display_name":"Bamako, Angers, Maine-et-Loire, Pays de la Loire, Metropolitan France, 49000;49100, France",
"class":"highway","type":"platform","importance":0.2,
"address":{"address26":"Bamako","city":"Angers","county":"Angers","state":"Pays de la Loire","country":"France","postcode":"49000;49100","country_code":"fr"},"namedetails":{"name":"Bamako"}},
In the address field/object you see "address26":"Bamako". What does that mean? the other keys all make sense.
If you access the osm id: (eg, http://nominatim.openstreetmap.org/details?osmtype=W&osmid=197528638), there is no mention of address26.
At the website: https://thefive.sabic.uberspace.de/ they have a number of address26 entries pointing to Nominatim. I don't know what their database represents.
I have come across other Nominatim search results with address29 instead of address26.
If you look at http://taginfo.openstreetmap.org/, you won't find address26 or address29 as keys or tags...
Once in a while you will see a city named "fixme" on an osm map, but at least you have an idea of what's going on there, address2[69] stumps me. Does anyone know why?