Signal Activities of Registered Nodes not from vcd, leading to Low Confidence power estimate

Hello,

I have recently synthesised my design in QuartusPro 21.3 targeting Agilex F-series and produced the .vo netlist file from EDA Netlist Writer, with 'simulation' tool name specified as VCS and language as Verilog. I then ran my testbench in VCS with`$dumpfile('file.vcd'); $dumpvars;` to produce the .vcd file which contains all the variables in top and submodules.

Now, with Power Analyzer settings configured with this .vcd and also default toggle rate for remaining signals as 12.5% (Thermal settings left as default), I obtained the attached Confidence Metric Details in QuartusPro. As shown in this screenshot, it shows that about 50.9% signal activities come from vcd, but 49% from Default Assignment, of which 78.1% are Registered. That means, of all the available registered nodes found in the netlist, signal activities of these 78.1% do NOT come from vcd.

But I am not sure why? Shouldn't VCS be able to measure the signal activities of these registered nodes, as it already identify the total number of registered nodes? But why QuartusPro thinks these should be Default Assignment instead?

My hope is that, solving my puzzle around Registered Nodes can help increase the Confidence Level of the power estimate by Power Analyzer.

Best regards,

Taihai