Sorry, that is incorrect.
No I don't think you understand those papers.
How were those spectrums obtained? By digitising the signal.
Yes you can generate a band width limited signal but unless you are going to send it through an other digitiser then there is no point.
If that assumption were true then you would get aliasing from a simple square wave oscillator which is clearly nonsense.
Any analog signal with a discontinuity in the wave- form (such as pulse train or sawtooth) or in the waveform slope (such as triangle wave) must be bandlimited to less than half the sampling rate before sampling to obtain a corresponding discrete-time signal. Simple methods of generating these waveforms digitally contain aliasing due to having to round off the discontinuity time to the nearest available sampling instant. The signals primarily addressed here are the impulse train, rectangular pulse, and sawtooth waveforms. Because the latter two signals can be derived from the first by integration, only the algorithm for the impulse train is developed in detail.
My red words. This is a signal that is about
to be digitised not one that has been generated and is being listened to. Which is what I took the OP to be asking about.
All of these assume that the analog DDS waveform is being produced by a DAC, rather than messing around with optimistic pulse width modulation hackery.
That makes no difference to what we are talking about here, it is just extra quantization noise outside the band we are interested in.