How to record "not recorded" for numeric fields?

[cjconroy]

For the NSF RANGES project, we are gathering tons of body measurements and reproductive remarks. As expected, many were not recorded. So, to avoid going back to the specimens or journals repeatedly to verify, how do people populate Arctos for, say, no weight taken? Can you put null in the field, but no weight taken in a remark? Or, just put no weight taken in a more general remark? Or in unformatted measurements which is alphanumeric? Hoping there is some reasonable precedent.