The 1977 footage.

The "shark" scene, added in 1977, starts about 35:31. (Timing based on Criterion 1977 DVD, 87 minutes.)
-Tati, looks different. His face has weathered.
-The film looks grainier.
-The 1977 sequences are obviously edited in with some of the 1951 sequences.
-The men on the beach are sporting long, post-Beatles hair.
-There is a zoom at 35:59, which was not an accepted or practical shot in the early 1950s. There were no other zooms in the rest of the movie.
-The Hotel appears to have had an extension added.

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The story is king.