You really need to validate the content of your format - that's something only you can do, given the large size and the limits of this forum environment.
One test to validate your SAS format is to unload it with PROC FORMAT and CNTLOUT= to a SAS file, for close inspection, as compared to your data file.
After doing a CONTENTS against the CNTLOUT= file to get familiar with it, review the SAS-generated variables START, LABEL, and HLO data values, to start, if you are working with explicit values in the format (rather than value ranges -- a bit more complicated).
Then sort your two files and do a MERGE in a DATA step. If you cannot get the MERGE to work, then you have some type of garbage in the format (determined from a PROC PRINT of START variable with a hex-type character display format.
Scott Barry
SBBWorks, Inc.
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