On 29 September 1977 the first space station of the second generation - Salyut-6 - was launched to orbit. The second docking port on it was the critical change, which led to rather different record - the station had 16 crews visiting and working on the station, compared to up to 3 visits to the previous stations. It also had 12 visits of automatic cargo spaceships - Progress - which was designed for that purpose.
The ship exchange practice was established, and it works like this. A crewed expedition arrives to an empty station, let's call their spaceship S-1. Then the second expedition arrives, docks to the second port with their spaceship S-2. When either of these expedition needs to leave first, they take S-1, leaving S-2 attached to the station. This way the S-2 has more time left staying in space. For example, if the first expedition was "long-term," and the second one was "visiting," the second one "delivers" a fresh spaceship to the first expedition, allowing them to stay in space longer that just one spaceship would allow. Soyuz spaceships have a design life staying in space, which is now longer than 6 months, but used to be much shorter. With such a ship exchange the expeditions could stay in space for even longer periods. Those space stays were significantly longer than what was available in 1960-s, when the limiting factor was more on the side of people, and not the spaceships.
This seemingly modest technical change - the second docking port - significantly changed the possible spaceflight programs. Salyut-6 also had a visit of unmanned Kosmos-1267, also known as TKS-2 - a large spaceship, nearly as big as the Salyut station itself, demonstrating the possibilities of potentially growing stations in space. Another important first - flight of Vladimir Remek, the first person not from USSR or USA in space, then Salyut-6 was visited by Miroslav Hermaszewski, Sigmund Jahn, Bertalan Farkas, Pham Tuan, Arnaldo Tamayo Mendez, Jugderdemidiin Gurragchaa, Dumitru Prunariu. This way space stations showed that they can host people from other nations.