I thought this was interesting.... the different sizes of the last 5 versions...... I think I might toss out x6-x8
From my reference notes:
"Plan Compatibility:
X9 does not support reading in plans with the .pl# or .la# extension (files from any versions older then Version 10 (2005). CA 10 (2005) creates *.plan files.). To open these older plans in X9, first open these files in X8 and save them which will be in the newer format as a .plan or .layout file. X8 will open plans back to Chief Architect 97 (released August 1997). Version 9 is required to open pre-August 1997 .pln files. Keep X