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Using the projection operator formalism, we derive an extension to the QRT that explicitly incorporates these correlation-induced corrections, enabling us to capture multi-time correlation functions in non-Markovian regimes. We apply this framework to the variational polaron master equation for the spin\u2013boson model in ohmic and super-ohmic regimes, where the polaron transformation mixes system\u2013bath degrees of freedom to produce a non-thermal effective environment. Benchmarking against numerically exact tensor-network simulations, we demonstrate quantitative agreement for single- and two-time observables, including linear-response spectra, even at strong coupling. Our approach broadens the reach of analytic master equations to multi-time observables in strong-coupling and non-Markovian regimes, where environmental memory effects and system\u2013bath correlations are crucial.<\/jats:p>","DOI":"10.1063\/5.0338834","type":"journal-article","created":{"date-parts":[[2026,8,18]],"date-time":"2026-08-18T15:47:06Z","timestamp":1787068026000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Beyond the quantum regression theorem in variational polaron master equations: From Ohmic to super-Ohmic environments"],"prefix":"10.1063","volume":"165","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2941-6643","authenticated-orcid":false,"given":"Matias","family":"Bundgaard-Nielsen","sequence":"first","affiliation":[{"name":"Department of Electrical and Photonics Engineering, Technical University of Denmark 1 , Building 343, 2800 Kongens Lyngby,","place":["Denmark"]},{"name":"NanoPhoton-Center for Nanophotonics, Technical University of Denmark 2 , Building 343, 2800 Kongens Lyngby,","place":["Denmark"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4578-6759","authenticated-orcid":false,"given":"Jake","family":"Iles-Smith","sequence":"additional","affiliation":[{"name":"School of Mathematical and Physical Sciences, The University of Sheffield 3 , Western Bank, Sheffield S10 2TN,","place":["United Kingdom"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"317","published-online":{"date-parts":[[2026,8,18]]},"reference":[{"key":"2026081811462205100_c1","doi-asserted-by":"publisher","first-page":"040405","DOI":"10.1103\/physrevlett.120.040405","article-title":"Operational Markov condition for quantum processes","volume":"120","year":"2018","journal-title":"Phys. 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