All flam definitions I know of consider it a sequence of only two notes/strikes whereas piano rolls can have more than two notes. Also flam is usually considered a drum rudiment.

Debatable whether doing something unintentionally on an instrument is always a sign of bad technique. Mastery and even great technique itself seem to 'accidentally' produce great things sometimes on an instrument (flow state, idea of finger smarts, etc.). Probably boils down to your definition of 'unintentionally'.

Yes I sometimes see the threshold for a tonal modulation given as one complete melodic or 'structural' phrase. That seems the least arbitrary to me so I go with it. For a metric/tempo modulation rather than just a temporary change of meter a complete 'section' seems as good a criteria as any to me. Perhaps where a section begins and ends could itself sometimes be up for grabs though? –

@jjmusicnotes yes I can hear the closeness of those perceived eighths. Perhaps as listeners we automatically give Johnny boy the benefit of the doubt and assume the fluctuation is because he means it. Or maybe maybe Winters saw all this coming and he's just playing with us. If so mission accomplished.

@jjmusicnotes : Yes, thanks - I'm just chewing over your answer below now. When you say 6/8 you mean (8 x eighth-notes pre-change) = (6 x eighth-notes post-change) right?

@jjmusicnotes: As no explanation was given by the down-voter, I still don't know for sure if this was the reason for the down-vote either, but originally I did miss-hear the change of tempo/metric modulation as ← half-note = dotted quarter-note → and have since edited the post. The tempo is a little shaky at the change and it threw me. Unfortunate that oftentimes down-voters aren't compelled to provide any reason for down-voting, as the generic info which pops up (poorly researched, not useful, non-sensical) isn't really much help.

So in this case , even though the new rhythm lasts a good few measures it generally wouldn't be considered a modulation as it doesn't last for at least the remainder of the section?

The guitar strums and bass rhythm mark out the skipple /shuffle pulse.

@Tim: Skipple is the term Wayne Chase uses ('How Music Really Works' Roedy Black Publishing) for the blues shuffle/triplet groove/swing/etc pulse because these terms each have their own connotations and end up being less than ideal descriptors. Seems it's not a recognised term, but in the absence of an alternative I use his term for it. youtube.com/watch?v=J-vhdGQjqNQ