Is the code length strictly defined? I would expect that as long as the string contains a "+" anywhere in the code, then any length (including odd) should be acceptable (provided the "text location context" such as "Hawaii" or "Honolulu" makes the code unambiguous). Maybe a degree symbol (°) could be optional after the first four digits.
Odd length is particularly useful closer to the poles, where cells are dramatically stretched N-S (longitude is substantially "taller" than latitude is "wide"). For example the Trivett weather station in Alert, Canada can be precisely pinpointed with 9 "digits" (C7JV FF2V+8) or 5 with local context ("FF2V+8 Alert, Canada"). You can pinpoint a hospital at "39+7 McMurdo, Antarctica"
If there is no "+" should the code imply the largest area (first "digits") or the local (fifth and subsequent "digits)? Does "85FQ Colorado" refer to Denver and a hundred kilometers SE or just a tiny section of empty road? I would think that Continents, Oceans, Countries, and maybe States would imply the largest area, whereas Cities and Mountain Peaks imply the local area.
Maybe a degree symbol could be optional such as "6G8V°W9M4+" or "8V°W9 Tanzania". After all, the four "digit" prefix does represent a square degree of area.