For a small recording scheme and a small number of iRecord occurrences (166) it seems a legitimate approach to download the iRecords into Recorder. Place them into a Survey and uncheck them all. Work through these at leisure, checking them and moving them to a checked Survey.
Aside from issues relating to other data incompatibilities (e.g. date separator in iRecord is "to" whilst Recorder only accepts "-") the major issue of interest is the Determination type and Verification status.
This falls into two parts:
1. What the recorder thinks
iRecord: Certain ***, Likely **, Uncertain * (=Possible), [blank] (those are the terms you get in a download)
2. How the verifier responds
iRecord has 6 verification terms (3 responses, each subdivided into 2):
Accepted: Correct, Considered correct
Not accepted: Unable to verify, Incorrect
Unconfirmed: Plausible, Not reviewed

Recorder has a different set of terms, Determination type. These must cover both the original recorder's determination and the verifier's response.
The following seem to be the most appropriate matches:
iRecord's "Certain" maps to Recorder's "Considered Correct"
iRecord's "Likely" maps to Recorder's "Unconfirmed"
iRecord's "Uncertain" maps to Recorder's "Requires confirmation"

The verifier may respond with any of the 6 Recorder terms, 3 of which should be reserved for the verifier (they're inappropriate for the recorder as they're asking an expert for an opinion): "Correct", "Considered incorrect" and "Incorrect"

In thread http://forums.nbn.org.uk/viewtopic.php?id=6087 it was suggested that the original recorder's determination should be retained.
Thus to add a verifier's response there are two options, one is to simply "check" and the other to add an additional determination (role = Specialist)