To find out if your SyncSort supports values from the PARM, can you run this and see what happens please.
//STEP0100 EXEC PGM=SORT,PARM='JP1"TEST"'
//SYSOUT DD SYSOUT=*
//SORTIN DD *
DOES NOT MATTER
//SORTOUT DD SYSOUT=*
//SYSIN DD *
It should either fail pointing at JP1, or it should produce TEST on the sysout for SORTOUT.
If it works, you would be able to provide a parameter to your SORT Control Cards. If it doesn't work, we'll do something else
Basically, we'll have, in some way, a SORT symbol that you can use in INCLUDE/OMIT COND= to select the records which are required.
Generating the symbols from the "current date" will also be possible, but we may be able to suggest something which is more flexible.