I cleaned it up some and you can download the Title project here:
https://fcpxtemplates.com/downloads/
I had run into some problems because you can do stuff in Motion that doesn't translate to FCPX for titles and/or effects. Particularly, you cannot retime clones to loop in anything but a generator, and a generator is overkill for this type of effect.
The basic principle is to create the months as separate text objects that are one frame long and spread out over 12 frames. Then clone that sequence and duplicate the clones over the project length. THEN, clone all of that so that it can be replicated. Once it is replicated, turning off Play Frames and using the Source Start Frame control will change the months as you increase its value.
A Numbers object with auto animation turned off is linked to the Replicator Source Start Frame slider will increase in value from 0 to 120 and using the Scale parameter, this can be scaled to increase in value by 1 every 12 frames (Scale = 0.0833333333). In order to make the "flip" from December to the next year on January, a Source Start Frame offset of 0.1 needed to be added. This works over the entire range that has been prepared for this title.
Another Numbers object is added and turned off, but *its* value is linked to the first Numbers with the Apply Mode set to Add to Source. This Numbers' value is published as the Start Year value.
So, the replicator and these two numbers objects are about all there is to the functionality of this title.
The Month text alignment is managed with an Align To behavior. I aligned the Upper Right corner of the Months to the Upper Left of the Year. I published the Offset parameter so you can customize the look as you like.
The default appearance of the setup is this:

I made the title 10 seconds long and the time span is 10 years. You can set any start year and the +Months slider will increment the year when it passes from December to January automatically.
I added a small selection of optional fonts for the Month label and a separate option to select the Font for the year. The smaller month font selection is due to the fact that you cannot link fonts between text objects and they had to be rigged.
You can adjust the Month Font Size and the Year Font Size separately as well with their colors.
You can make an alternate version of abbreviate Months -- just go through the original "month labels" and shorten them. (You could even create these, along with numerical months, as alternative (and publishable) versions since the Clone of the labels will automatically copy whatever is shown for those original 12 frames. Just select the Jan through Dec Text objects and group them, then start another group with your alternative content, etc. Add their respective opacities (just the groups) to a popup menu rig and you'll have even more customization control.
I originally planned to just write out the recipe, but parts of this build are ... really tedious ... and wouldn't really translate well as a recipe.
HTH