Shell: Generate a filename by appending a variable

A file name that I am receiving has 3 parts to it.

• Prefix: foobar_
• date: 2015-12-31_
• filenum: 100.dat

Putting them together we get foobar_2015-12-31_100.dat. Currently picking out files with today's date and correct filenum works. So, the next filenum is 101. Please examine script to understand.

  echo "Checking for file"
  DBNR=`mysql -uroot -p$DBPWD test_schema -sNe 'SELECT max(file_id) FROM filenumbers WHERE filetype="D"'`
  echo "Last number is: ${DBNR}"
  NEXTNUM=$((DBNR+1))
  NEXTFILE="foobar_${TODAY}_${NEXTSEQ}.dat"

  echo ">>>>> NEXT FILENAME: ${NEXTFILE}"  # $TODAY is optional

  if [ -f "${NEXTFILE}" ]; then
    echo ">>>>> Correct file exists!"

  else echo "Incoming dir is not empty but expected file is not present."

The line where NEXTFILE is is generating for a specific file but comment states $TODAY is optional. How do I then exclude $TODAY so that the if-statement below will evaluate to true for file names:

• foobar_2016-02-01_101.dat, or
• foobar_2016-01-30_101.dat, or
• foobar_2016-02-02_101.dat?

and evaluate foobar_2016-02-01_102.dat to false?