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The first number is the for "old" file while second is the "new" file. Every row after this seems to have a different value for LIVETIME. The other run 633997253 shows the same behavior. The fdiff utility doesn't report any other differences in the data (e.g, the number of photons in the files are the same).
According to the confluence page On FT1 Livetime: "So for now, the LIVETIME values in the FT1 files should be ignored. Again, they are not currently used by the Science Tools, and in particular do not affect calculations of exposure, which are made with the livetime accumulations in FT2 files."