One body, one basic layout, three engines across almost three decades: a 594 cc flat-twin at launch in October 1972, enlarged to 652 cc in 1977 at an unchanged claimed output, and finally a water-cooled 704 cc unit from 1987 in the hatchback-bodied 126 BIS, which also brought the car’s only real structural change: a rear hatch, replacing the boot lid, over an engine that stayed exactly where it had always been.[1] Fiat built it in Italy until 1980; FSM in Poland kept building it, under licence and then as Fiat Auto Poland, for twenty more years after that.
Most of what is verifiable and precisely dated in the source concerns the Polish-market 126p rather than the original Italian car, which is reflected here in the market-variant naming on each trim rather than in separate entries; the underlying mechanical specification is the same car under both names.