The 12 bar blues forms

Hi everyone,I came across a problem when studying the 12 bar blues progression. So ususally,  the 12 bar blues structure goes by the below patten.

The first 4 bars just use the I chord - I, I, I, I.

The middle 4 bars go IV, IV, I, I.

And the last 4 bars go V, IV, I, VHowever, when I am studying the "My Blues Bending Song Example #4",I just cant't make sense of the why the stucture goes from V, IV, I, IV, V. It looks to me have to do with the song starting from the V (Five Chord). But it just looks so different from the sequence I'm familiar with.It would be much apperaciated if anyone can explain the 12 bar blues varioations. Thanks!