Hi Anna,
I'm reaching but applying logic, look at it this way, I guessed correctly they had been resoled, enhanced the head dress logo as much as I could and "40 " was the euro size-- then just maybe 5-91 is May 1991 in that combination of numbers on the boots.
And I do think they are Alligator Skin, not embossed but a bit hard to tell.
Not a great rule of thumb but maybe, as you have the boots, think, eyes closed,, running your thumb/finger across paving slabs, you would feel and sense depth of cravises, croc' & alli' skin is the same, where the scales join, most embossing doesn't have this, the crevices are almost shallow/smoothe.
Some of my croc' and alli items--you almost fall in, well thumb does.