How could San Marino's governemnt remain unchanged if the following is true?

From www.historychannel.com:

San Marino claims to be Europe's oldest existing state. According to tradition, in the 4th cent. A.D. Marino, a Christian stonecutter, took refuge on Mt. Titano, the chief geographical feature of San Marino. A community was formed by the mid-5th cent. and its independence recognized by the papacy in 1631. San Marino volunteers served with the Italians in both world wars, and Allied aircraft bombed the tiny republic in 1944. Following a period (1947-57) of Communist-led coalition governments, a series of coalitions headed by Christian Democrats held sway until 1978, when a Communist-led coalition again came to power. A coalition of Communists (renamed Progressive Democrats in 1990) and Christian Democrats governed the country from 1986 to 1992, when the Christian Democrats formed a coalition with the Socialists.

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If this is true, then San Marino's government has definitely changed since the US was founded. I would say it's changed in the past 20 years.

Please set me straight if I am wrong. I just want to make sure I'VE got it right.

Thanks
--Thom