sub-second resolution timestamps on files in encfs

i have a file system used for a few things that uses encfs, a sorta-secure file system that presents clear files at its mount point and stores them encrypted (or the reverse). anyway, this evening i stored 299 PNG image files there. when i listed them with --full-time i could see that 297 of them have .000000000 for the fraction of seconds time and 2 of them do not. the 2 that do not have .138837108 and .020323306 there. that's full nanosecond capability, not limited to microseconds as some older file system types do. but my curiosity is why just 2 out of 299. if i had stored a 400th file would it have had nanoseconds, too, to make a nice rounded 1 out of 100?
Code:lt2a/forums /home/forums 12> ls -l --full-time /home3/st/all|fgrep 20201204|fgrep -v .000000000
-r-------- 2 st st 1350712 2020-12-04 01:22:59.138837108 -0500 20201204012258600378036.png
-r-------- 2 st st 1289245 2020-12-04 18:20:13.020323306 -0500 20201204182012634775638.pngCode:ls -l --full-time /home3/st/all|tail -n4
-r-------- 2 st st 1158883 2020-12-04 21:41:41.000000000 -0500 20201204214141668525934.png
-r-------- 2 st st 1553289 2020-12-04 22:53:13.000000000 -0500 20201204225313375955820.png
-r-------- 2 st st 1499090 2020-12-04 22:53:19.000000000 -0500 20201204225319168496847.png
-r-------- 2 st st 1503221 2020-12-04 22:53:21.000000000 -0500 20201204225321631628036.png