Well, just looking at this handy chart for marine isotope stages we can see that the last few interglacials actually appear at MIS 5 (specifically 5e) and several substages of MIS 7. The letter notation for substages used in the diagram is the best concerted effort to tidy up all the local minima/maxima into a consistent scheme, as originally published by Railsback et al⁽¹⁾ and is pretty much in wide use now.

Lisiecki, L. E., and Raymo, M. E. (2005), A Pliocene‐Pleistocene stack of 57 globally distributed benthic delta O‐18 records, Paleoceanography, 20, PA1003, https://doi.org/10.1029/2004PA001071

Railsback, L. B., Gibbard, P. L., Head, M. J., Voarintsoa, N. R. G., and Toucanne, S. ( 2015), An optimized scheme of lettered marine isotope substages for the last 1.0 million years, and the climatostratigraphic nature of isotope stages and substages, Quat. Sci. Rev., 111, 94– 106, 10.1016/j.quascirev.2015.01.012