Revising the past, in the past

As an afterthought to this morning's post, the graph below is reproduced from the Economic Report of the President, 1977 (PDF) from FRASER:

Potential GNP 1964-1977, Old and New ("new" = 1977)

The thing is so old it uses GNP, not GDP. Note the "old" trend line and the "new" one. The new one is lower, just like with Altig and Gavin's graphs. For the 1977 Report of the President, they revised the past back to 1964.