The history fields in the equivalent *_1849_2015_ESM1*.nc files reveal some of the processing used to create these files:
$ for f in *_1849_*_ESM1*.nc; do echo; g=${f/.nc/.anc}; ls -lh $f $g; ncdump -ht $f | grep history; done 2>&1|more
-rw-r--r-- 1 txz599 p66 224M Jan 15 2019 BC_hi_1849_2015_ESM1.anc
-rw-r--r-- 1 txz599 p66 213M May 30 2019 BC_hi_1849_2015_ESM1.nc
:history = "Thu May 30 14:41:38 AEST 2019 - XCONV V1.92 16-February-2006" ;
-rw-r--r-- 1 txz599 p66 443M Jan 15 2019 Bio_1849_2015_ESM1.anc
-rw-r--r-- 1 txz599 p66 852M Dec 19 2018 Bio_1849_2015_ESM1.nc
-rw-r--r-- 1 txz599 p66 224M Jan 15 2019 OCFF_1849_2015_ESM1.anc
-rw-r--r-- 1 txz599 p66 426M Dec 19 2018 OCFF_1849_2015_ESM1.nc
-rw-r--r-- 1 txz599 p66 338M Jan 16 2019 ozone_1849_2015_ESM1.anc
-rw-r----- 1 txz599 p66 85M Jan 15 2019 ozone_1849_2015_ESM1.nc
o3:history = "From O3_CMIP6_1849-2015" ;
:history = "Thu Nov 8 12:30:17 2018: ncrename -v ozone_zonal,o3 ozone_hist.2d.nc\n",
ls: cannot access 'scycl_1849_2015_ESM1.anc': No such file or directory
-rw-r--r-- 1 txz599 p66 1.7G Dec 19 2018 scycl_1849_2015_ESM1.nc
-rw-r--r-- 1 txz599 p66 881M Jan 16 2019 scycl_1849_2015_ESM1_v4.anc
-rw-r--r-- 1 txz599 p66 1.7G Jan 15 2019 scycl_1849_2015_ESM1_v4.nc
$ ls -hl ozone_hist.2d.nc; ncdump -ht ozone_hist.2d.nc | grep history
-rw-r----- 1 txz599 p66 85M Jan 14 2019 ozone_hist.2d.nc
o3:history = "From O3_CMIP6_1849-2015" ;
:history = "Thu Nov 8 12:30:17 2018: ncrename -v ozone_zonal,o3 ozone_hist.2d.nc\n",
The file O3_CMIP6_1849-2015* is not in /g/data/p66/txz599/data/ancil/CMIP6/.