These are single continuous flights, not cumulative time: the clock starts at launch and stops at landing. Only one of the five was made by a crew that did not fly on Mir or the International Space Station, and the record has stood for three decades.
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437.7 days — Valeri Polyakov, Mir, 8 January 1994 to 22 March 1995. Still the record. Polyakov was a physician, and the flight was designed partly to answer a question a Mars mission would have to answer: can a human stay in weightlessness for a year and a half and still walk on arrival? He returned in good health, and the mission remains the benchmark for long-duration medicine.
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379.6 days — Sergey Avdeyev, Mir, 13 August 1998 to 28 August 1999. The second-longest single flight and, for years, part of the largest cumulative total ever flown: 747 days across three missions. He spent the long stay running experiments on the ageing station while it was kept aloft by visiting crews.
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373.8 days — Oleg Kononenko and Nikolai Chub, ISS, 15 September 2023 to 23 September 2024. The longest ISS expedition, and the first to pass a year without the Mir-era rotation that made Polyakov's flight possible. Kononenko spent his 1,000th day in space during the mission; he now holds the all-time record for cumulative time, 1,111 days over five flights.
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370.9 days — Sergey Prokopyev, Dmitry Petelin and Francisco Rubio, ISS, 21 September 2022 to 27 September 2023. Their ride home, Soyuz MS-22, was punctured by a micrometeoroid in December 2022 and lost its coolant; the replacement MS-23 flew up empty, and the crew stayed an extra six months while it was prepared. Rubio's 371 days set the US record for a single flight.
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365.9 days — Vladimir Titov and Musa Manarov, Mir, 21 December 1987 to 21 December 1988. The first flight to last a full year, and the one that proved a year in orbit was survivable. The crew launched and landed on the same calendar date and spent much of the mission monitoring their own bodies for the changes a Mars trip would have to survive.
A Mars mission needs six to nine months each way plus time on the surface: two to three years in total. Polyakov's 437 days remains the closest thing to a rehearsal, and the fact that nobody has gone longer since is not for lack of interest — it is because nobody has needed to yet.