Experimental results (recent IR, DFT calculations and modern multinuclear NMR measurements on Rh-containing clusters, together with earlier VT multinuclear NMR measurements) show that the use of the Ligand Polyhedral Model (LPM) to provide a general mechanism for ligand fluxionality in Transition Metal Carbonyl Clusters (TMCCs) in solution cannot be sustained; instead there are numerous examples of only partial CO-migration over either part or sometimes the whole of the Rh-polyhedron as well as rhodium and carbonyl polyhedral rearrangements of Rh9- and Rh10-TMCCs containing an interstitial P when, in the high temperature limiting spectra, all the metals and all the carbonyls become equivalent and show time-averaged values of (1)J(Rh-P) and (2)J(P-CO) respectively.