...
   TESTS
       Some  tests,  for  example  -newerXY and -samefile, allow comparison between the file cur‐
       rently being examined and some reference file specified on the command line.   When  these
       tests  are used, the interpretation of the reference file is determined by the options -H,
       -L and -P and any previous -follow, but the reference file is only examined once,  at  the
       time  the  command line is parsed.  If the reference file cannot be examined (for example,
       the stat(2) system call fails for it), an error message is issued, and find exits  with  a
       nonzero status.

       Numeric arguments can be specified as

        +n     for greater than n ,

       -n     for less than n,

       n      for exactly n.
...

## fix modification time of file by file name
## add -c or --no-create for non exists files
$ for i in {01..12}; do echo $i;touch -c -m -t 201906${i}0122 file_name_201905$i.csv;done
01
02
03
04
05
06
07
08
09
10
11
12

## show results
$ ls -l
итого 0
-rw-r--r-- 1 lejnin lejnin 0 июн  1 01:22 file_name_20190501.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  2 01:22 file_name_20190502.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  3 01:22 file_name_20190503.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  4 01:22 file_name_20190504.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  5 01:22 file_name_20190505.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  6 01:22 file_name_20190506.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  7 01:22 file_name_20190507.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  8 01:22 file_name_20190508.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  9 01:22 file_name_20190509.csv
-rw-r--r-- 1 lejnin lejnin 0 июн 10 01:22 file_name_20190510.csv
-rw-r--r-- 1 lejnin lejnin 0 июн 11 01:22 file_name_20190511.csv
-rw-r--r-- 1 lejnin lejnin 0 июн 12 01:22 file_name_20190512.csv

## find mtime greater then 6 days
$ find . -mtime +6 -print | sort 
./file_name_20190501.csv
./file_name_20190502.csv
./file_name_20190503.csv
./file_name_20190504.csv
./file_name_20190505.csv

## remove its
$ find . -mtime +6 -print -exec rm -f {} \;| sort 
./file_name_20190501.csv
./file_name_20190502.csv
./file_name_20190503.csv
./file_name_20190504.csv
./file_name_20190505.csv

## show
$ ls -l
итого 0
-rw-r--r-- 1 lejnin lejnin 0 июн  6 01:22 file_name_20190506.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  7 01:22 file_name_20190507.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  8 01:22 file_name_20190508.csv
-rw-r--r-- 1 lejnin lejnin 0 июн  9 01:22 file_name_20190509.csv
-rw-r--r-- 1 lejnin lejnin 0 июн 10 01:22 file_name_20190510.csv
-rw-r--r-- 1 lejnin lejnin 0 июн 11 01:22 file_name_20190511.csv
-rw-r--r-- 1 lejnin lejnin 0 июн 12 01:22 file_name_20190512.csv

$ cat t.sh
#!/bin/bash
FILEMASK=file_name_
for yyyy in `date +%Y` $(((`date +%Y` - 1 )))
do for mm in {01..12}
  do for dd in {01..31}
   do 
MYDT=${yyyy}${mm}${dd}
MYFILE=${FILEMASK}${MYDT}.csv
test -w $MYFILE && touch  -m -t ${MYDT}0122 $MYFILE
   done
  done
done

find . -name ${FILEMASK}'20[0-9][0-9][01][0-9][0-9][0-9].csv' -mtime +13 -print

{01..31}

01 02 03 ... 31

$(((`date +%Y` - 1 )))

$(expr `date +%Y` - 1)