How to synch up series with missing data?

The OLD EXCEL WAS INTUITIVE to use. OK, the new one may be easy, if not intuitive, but I cannot find the features I am looking for.

I have an existing chart already, I added additional series to it.

When the series contains all the data, of course, that's trivial and it plots correctly.

When the series contains missing data, the series plots in the wrong location!
It SHOULD appear shifted to the right, synchronizing on the common values of the X axis. Instead, it plotting data points on a first come first served basis.

See attached. I sketched in where the data SHOULD be plotting.

I have hand typed these values, so I don't expect any "data type" or "data format" issues, which I already know can cause bogus results. I cannot see the problem though.