When using SMF-Records for XCOM transfers it might happen that for files having a size larger than 4GB that size is displayed incorrect in the SMF-Record.
The size ("NUMBER OF UNCOMPRESSED BYTES") is stored in field SMF#UNCB of the SMF-Record. As this field has Fullword-length it cannot contain entries larger than 4GB. For that new field SMF#UNC2 ("NO. OF UNCOMPRESSED BYTES EXT") was created. This field is incremented by one every time field SMF#UNCB overflows. So when you interpret both fields SMF#UNC2 and SMF#UNCB as one field of two Fullword length you have the correct size.
The same is true for the number of compressed bytes. Here you have field SMF#CMPB ("NUMBER OF COMPRESSED BYTES") and field SMF#CMP2 ("NO. OF COMPRESSED BYTES EXT") if the size does not fit into SMF#CMPB alone.
So when you interpret both fields SMF#CMP2 and SMF#CMPB as one field of two Fullword length you have the correct number of compressed bytes.