multiply labelled

https://doi.org/10.1351/goldbook.M04063
A @[email protected] compound may be multiply labelled when in the unmodified compound there is more than one atom of the same element at the position where the isotopic modification occurs, e.g. H in CH4, or there are several atoms of the same element at different positions where the isotopic modification occurs, e.g. C in C4H8O.
Sources:
Blue Book, p. 515 [Terms] [Book]
PAC, 1981, 53, 1887. (Nomenclature of inorganic chemistry: II.1 - Isotopically modified compounds) on page 1893 [Terms] [Paper]