Stripline reference plane discontinuity in reference design
You can route across a cut up plane with no issues as long as each cut up plane is paired with a tightly coupled solid (gnd) plane -and- you engineer the PDN (bypass network) to have sufficiently low impedance between all power plane islands and ground (use something like my PDNtool.com for this).

If you make the cuts wider than about 1/3 the electrical length of the rise/fall time of your signals, you will start to see some reflections due to the lower capacitance. This can easily be simulated if you have access to an IBIS simulator.

Also the plane nearest to your stripline traces will "dominate", so if that is solid you have no issues either.

PS: Reference boards are not holy. There are MANY reference boards out there with lots of serious design errors. So watch out!

Does that answer your question?