This article outlines if the os-package missing from the show version is expected or not.

The “os-package” is designed to contain the latest version of the package system and is installable on any BSDX version (FreeBSD 10 or later) of Junos OS Release 15.1 or later. Please find the JUNOS release starting with FreeBSD 10 or later for platforms here. The package is architecture-neutral and check out TSB70152 [juniper.net] for more details on os-package and its installation.

The below show version output from RE1 is missing the os-package file while both REs are running the same version:

labroot@mx960> show version invoke-on all-routing-engines | no-more
re0:
--------------------------------------------------------------------------
Hostname: mx960
Model: mx960
Junos: 20.4R3-S2.6,os-package-20231117 ----------------------------------------------------------> Here
JUNOS OS Kernel 64-bit [20211117.c779bdc_builder_stable_11-204ab]
JUNOS OS libs [20211117.c779bdc_builder_stable_11-204ab]
JUNOS OS runtime [20211117.c779bdc_builder_stable_11-204ab]
JUNOS OS time zone information [20211117.c779bdc_builder_stable_11-204ab]
JUNOS network stack and utilities [20220206.163424_builder_junos_204_r3_s2]

re1:
--------------------------------------------------------------------------
Hostname: mx960
Model: mx960
Junos: 20.4R3-S2.6 ---------------------------------------------------------------------------------------> Here
JUNOS OS Kernel 64-bit [20211117.c779bdc_builder_stable_11-204ab]
JUNOS OS libs [20211117.c779bdc_builder_stable_11-204ab]
JUNOS OS runtime [20211117.c779bdc_builder_stable_11-204ab]
JUNOS OS time zone information [20211117.c779bdc_builder_stable_11-204ab]
JUNOS network stack and utilities [20220206.163424_builder_junos_204_r3_s2]

os-package is used for FreeBSD upgrade. Once upgraded, it is no longer needed or can be deleted from the package list. 

Verify the REs FreeBSD version via the below outputs:
labroot@mx960> start shell
% uname -rsm
FreeBSD JNPR-11.0-20211117.c779bdc_buil amd64

labroot@mx960> request routing-engine login backup
Last login: Wed Sep 11 23:06:28 from re0
--- JUNOS 20.4R3-S2.6 Kernel 64-bit JNPR-11.0-20211117.c779bdc_buil

{backup}

labroot@mx960> start shell

% uname -rsm
FreeBSD JNPR-11.0-20211117.c779bdc_buil amd64
Last login: Tue Feb 27 05:16:25 from re1
--- JUNOS 20.4R3-S2.6 Kernel 64-bit JNPR-11.0-20211117.c779bdc_buil

OR

labroot@mx960> show version invoke-on all-routing-engines | no-more
re0:
--------------------------------------------------------------------------
Hostname: mx960
Model: mx960
Junos: 20.4R3-S2.6,os-package-20231117
JUNOS OS Kernel 64-bit [20211117.c779bdc_builder_stable_11-204ab]

re1:
--------------------------------------------------------------------------
Hostname: mx960
Model: mx960
Junos: 20.4R3-S2.6 
JUNOS OS Kernel 64-bit [20211117.c779bdc_builder_stable_11-204ab]

If both REs are using the same FreeBSD version, it is ok if the os-package is not shown in the show version of the backup RE.