big files on google compute engine instance, ubuntu 18.04

[Gary Aitken]

The biggest files on my google compute engine (ubuntu-18.04) are snap related:

./var/lib/snapd/seed/snaps:
132452 google-cloud-sdk_161.snap

./var/lib/snapd/snaps:
156580 google-cloud-sdk_170.snap
156068 google-cloud-sdk_169.snap

./snap/google-cloud-sdk/170/bin:
141253 anthoscli

./snap/google-cloud-sdk/169/bin:
141253 anthoscli

Are any of these safe to delete?

In particular, is any snap with a lower number guaranteed to be obsolete,
and therefore deletable?

   e.g. google-cloud-sdk_161 and 169 above?

Some of these, although older, are mounted for some reason:

Filesystem     1K-blocks    Used Available Use% Mounted on
udev             1993128       0   1993128   0% /dev
tmpfs             402992     952    402040   1% /run
/dev/sda1        9983232 8317076   1649772  84% /
tmpfs            2014956       0   2014956   0% /dev/shm
tmpfs               5120       0      5120   0% /run/lock
tmpfs            2014956       0   2014956   0% /sys/fs/cgroup
/dev/loop2         56832   56832         0 100% /snap/core18/1944
/dev/loop4         31872   31872         0 100% /snap/snapd/10707
/dev/sda15        106858    3686    103173   4% /boot/efi
/dev/loop1         56832   56832         0 100% /snap/core18/1988
/dev/loop5         31872   31872         0 100% /snap/snapd/11036
/dev/loop0        156160  156160         0 100% /snap/google-cloud-sdk/169
/dev/loop6        156672  156672         0 100% /snap/google-cloud-sdk/170
tmpfs             402988       0    402988   0% /run/user/1001

Why is a not-most-recent snap mounted?

The files in /var/lib/snapd/seed/snaps seem old and no longer used;
is there anything sacred about the /var/lib/snapd/seed/snaps contents?

/var/lib/snapd$ ls -l seed/snaps
total 220952
-rw------- 1 root root  58052608 Dec 11 09:35 core18_1932.snap
-rw------- 1 root root 135630848 Dec 11 09:35 google-cloud-sdk_161.snap
-rw------- 1 root root  32571392 Dec 11 09:35 snapd_10492.snap

Thanks,

gary