Good morning,
I upgraded to openSUSE leap 42.1 about a year ago.
Since then, I have been running all the recommended updates every Monday.
However, I have not found any new update for about a month (via YaST Control Center > Online Update).
Is this normal?
Hi and welcome to the Forum 
Yes, it’s normal for an End Of Life release… 
You need to look at upgrading, Leap 42.3 will be release soon.
Hi,
Leap 42.1 reached end of its lifetime on May 17th 2017 (https://en.opensuse.org/Lifetime).
Leaps version number has two components: “major.minor”. Major (‘42’ right now) displays what SLE core it is based on (SLE12 in this case - SLE + 30 = 42; this will change with next SLE and Leap which both will use 15 as their major version number) while the minor version number can be seen as a “Service pack”. 42.1 is the opensuse equivalent to SUSE’s SLE12SP1, 42.2 aligns with SLE12SP2.
You should upgrade to Leap 42.2 (current) or skip 42.2 and go straight to 42.3 (official release is tomorrow). There are several ways to upgrade your system https://en.opensuse.org/SDB:System_upgrade, I recommend you create a Leap 42.3 installation medium (usb-stick) and chose ‘Upgrade’ in its “boot menu” as this is the easiest way to upgrade. You can also change the repos and run “zypper dup” as described in the wiki entry.
Thank you very much for the detailed replies.
I will upgrade soon!