NADA package/cenboxplot() method: maximum censored percentage

One set of data has censored (less-than detection limits) water chemistry
concentrations for 80-100% of all observations. My initial trial-and-error
attempts to apply the cenboxplot() method suggests that it has an upper
limit to the percentage of censored observations. I do not see this limit in
Dennis Helsel's second edition.

   Has anyone experience plotting censored data and can provide me with the
maximum percentage of censored data in a set of observations?

TIA,

Rich