I guess a person could use a oscillating saw, carefully slide it up behind the siding to cut the finishing nails. Then slip a dog ear flashing up behind? No caulking needed then.
I did the same thing only when the flashing hit the nails, I tapped it a little and brought it back down and knoched a couple of nail width slots, to go up further, in the metal and used polyseamseal caulk, I think it was, for ease of sliding, strong holding and fast drying and only slight prying…never broke one.
In 30 years as a carpenter, installing all sorts of siding, I was never once provided with a copy of the manufacturer’s installation instructions or a copy of any code provision relating to siding, nor has anyone I ever worked with in all that time. Installation methods were all handed down by word-of-mouth, so much as I hate to admit it, for cementitious and composite siding, we did it wrong for a long time, much of this in S. CA in housing tracts up to 200 houses.
It’s unfortunate, and I feel kinda bad, but most of those issues were not crucial and I’m sure were repeated over most of N. America. With that in mind I wouldn’t make a big deal out of flashing missing from behind butt joints anymore than I would inadequate gaps between siding and vertical trim (⅛" for HardiPlank and 3/16" for composite) which is extremely common. If I mentioned these at all, I’d be sure to say whether I saw any problem connected with it.
A strip between siding joints, sounds cool. Don’t remember ever seeing one in my area.
But its only been 35 yrs+