Thomas Barthel's transliteration system does not always allow unambiguous reference to every sign encountered. For instance, it is impossible to specify which "adornment" is represented by suffixes ^o and s (see the list of affixes); the heads of the anthropomorphic series 200-299 sometimes lack one protrusion or both, which Barthel's system has no way of expressing; etc. Barthel's system is thus essentially lossy.

The Rongorongo Commission of the Cercle d'Études sur l'Île de Pâques et la Polynésie (C.E.I.P.P.) has attempted to reduce the lossiness of Barthel's system with these changes and additions:

• Code numbers are zero-filled to three digits to facilitate computer-processing. E.g. 1 becomes 001, 90 becomes 090.
• The distinction between variants and derivations is abandoned as redundant. Barthel's original variants or derivations are expressed by a capital V, suffixed. E.g. V451 and D9 become 451V and 009V.
• The absence of a protrusion from the type-2 head on the reader's right, left, or right and left sides is expressed by suffixing i, j, or k respectively.

  E.g.

• e and g are added to the list of suffixes (a to d) distinguishing between signs sharing the same code number.
• The ill-defined distinction between linking and merging is abandoned in favour of linking.
  E.g. becomes, after application of the other enhancements of this extended system, 305fs.020ey.
• Separate stacking and linked stacking are distinguished, the former expressed by a colon, as in the original system, the latter by a semicolon.
  E.g. becomes 043:050 and becomes 009;008.