I consider that several uses of the spell would overlap and that, as indicated by the rules, the strongest current effect would be applied … So, I made a simple table considering how 2 uses of 39; mirror images in sequential turns would work and how the attacks would affect them. The colors represent from which of the spells used is the image currently seen.
In this case, the colors represent each use of the "Mirror Image" spell, that is to say that each time a spell slot and an action were spent to cast the spell (in the 39; example, the spell was cast twice, the first time on turn 1, and the second time on turn 2).
The blue color represents the images created by the first use of the spell (I called it "A"), and the green color represents the images created by the second use of the spell (I called it "B" ").
The column "Total visible images that the enemy sees in the current round" represents the amount of mirror images that would be visible to people watching the caster, and the colors of the cells in this column are used to indicate if the images come from the first use of the spell (A) or the second use of the spell (B).
To summarize, the main mechanical effects of two subsequent uses of the fate of mirror images would be the following:
1st: Two turns must be spent to cast the spells.
2nd: Each group of images would have "an extra life" (which means that each "amount of image" should be "killed" twice to reduce the amount of images by 1).
The second effect is important because it represents a very interesting momentary buff for the escape of the caster, taking into account the effects of having the highest number of duplicates for a longer period.
Here is a copy of part of the spell description that indicates the chances of redirecting an attack to one of the duplicates, depending on the number of duplicates still visible:
If you have Three in duplicate you have to launch a 6 or more switch
the target of the duplicate attack. With of them duplicates you have to roll
a 8 or more. With a in duplicate you have to launch a 11 or more.
Basically, each use of the spell gives the caster an additional turn from each group of duplicates or an additional attack in the same turn from each group (the group of 3 duplicates, the group of 2 duplicates and the group of 1 duplicate).
It's also worth considering that maybe 3 or more subsequent uses of the spell could also be relevant, but only until the number reaches 10 (that's when the first use of the spell would expire naturally and the subsequent uses of the spell would not overlap more than 10 at a time, with one use of spell expiring on each subsequent turn – which would force the caster to spend his action casting the spell over and over again, each turn to keep the 10 "lives" for his group of 3 duplicates). The number "10" is however relevant, because in this turn, after having cast the spell 10 times, the caster could receive 10 attacks without reducing its quantity of 3 visible images (which maintains the highest chances of redirecting the attacks towards one of the images). even if the 10 attacks each succeed in "killing" an image). Think of it as an extremely situational landscape where the caster has 10 turns to prepare to rush into an extremely dangerous area with lots of potential enemies (not to mention the huge amount of locations spells / scrolls or other forms of casting that spell that would be necessary). I am not sure to make a chart for this, but I think the idea is quite funny.