Many thanks!
You got me onto the right path. For anyone else reading, I think the issue is that my Content Block was set to a specific width (1200px), while my Title was set to Wide Width.
But adding additional blocks, like Date, didn’t offer me an obvious width option. However, putting in a Column block, setting that to the same specific width (1200px) and adding the Date block inside that did the job.
Thanks again for your help.
