Eg. D0 with 10ns period and D1 with 20ns period have sync point at 20ns.

Please look carefully how the PULSE spice function is defined. The pulse width (6th param) is the duration of the top edge of the pulse, while normally we use the 50% value pulse width. To create a perfectly 50% duty cycle for example you need to subtract one rise time from the pulse width. See exampels below. Second waveform is perfectly 50% duty cycle if measured at half height.

Ah thanks for that reference. I checked https://www.seas.upenn.edu/~jan/spice/spice.overview.html and the spec says how the duty cycle of a pulse is defined as Tr + PW + Tf. When I subtract 100ps from the PW they all align. Thanks for another Sunday lesson

The new functions (prev(), del() )need some tests, so if you find something unusual please report :-)

I will!