What is the maximum dynamic range of an N bit signal?
From taking a look at the presentation, it seems that they might be using a slightly different definition of dynamic range than is typical. Usually, as in the Wikipedia article on the topic, dynamic range is defined as:

$$
\text{dynamic range} = \frac{\text{largest possible representable value}}{\text{smallest possible representable value}}
$$

For an $N$-bit (unsigned) signal, this is equal to:

$$
\text{dynamic range} = \frac{2^N-1}{1} = 2^N-1
$$

However, their discussion of dynamic range is interspersed with discussion of quantization noise. Therefore, I posit that they instead define dynamic range as:

$$
\text{dynamic range} = \frac{\text{largest possible representable value}}{\text{largest possible quantization error}}
$$

For a uniformly-quantized quantity such as this, the maximum quantization error is equal to half of one bit. That leads to a dynamic range of:

$$
\text{dynamic range} = \frac{2^N-1}{0.5} = 2(2^N-1)
$$

The extra factor of 2 gives you an approximate increase of 1 bit in "dynamic range" when measured this way.  I assume that's what is meant by an $N$-bit digitized signal providing $N+1$ bits of dynamic range.