However, sometimes zoom level 20 isn’t enough. Here:
is part of Nottingham at zoom level 20. At least one of the office names doesn’t appear (it corresponds to here in OSM). The problem is that the way that the “standard” renderd stores metatiles means that only a certain number of tiles can be stored for each zoom level (see this list post for the details). In order to store more I changed renderd slightly so that more zoom levels can be stored - see here and here for the details.
Rendering works fine at higher zoom levels (up to 28 in my example) so that all of those office names now appear. Here’s the same area at zoom level 21:
The principle could be extended to an eventual goal of 1:1 to keep Melchett and Darling happy (roughly zoom level 32 at this latitude) but that seems unnecessary even to me currently.