The accuracy of CVP measurements depend on how close the tip of the catheter is to the cavo-atrial junction where central venous catheter tips used for CVP should lie. MAC and Cordis are shorter catheters with tips that do not typically extend close to the cavo-atrial junction. If you are referring to Single Lumen Infusion Catheters (SLIC) inserted through the Swan-Ganz port, I would say that they could accurately measure CVP because they are longer than the length or the Cordis. The SLIC tip extends beyond the tip of the Cordis and can be as close to the cavo-atrial junction as a regular Multi-Lumen CVC that is not a Cordis or MAC. Our facility does not use SLIC's by the way, we use DLIC's which has the advantage of having 2 lumens and locks in place better than the SLIC's. We find that the DLIC's work better in preventing accidental dislodgement.
This website has a picture of a SLIC locked into place over a Cordis and you can see how the SLIC tip extends beyond the length of the Cordis:
Arrow International - combining technology and product innovation
This is a hospital website (not where I work) that advocates CVP measurement through the SLIC:
Single Lumen Kit :: Kit Types Section :: Internal Jugular Vein Central Venous Catheter Insertion