Hi Spirodonov,
First of all: don't worry, your English is pefectly understood.
According to my present knowledge, and as I posted here earlier, the hole in the butt stock was for keeping the gun supended muzzle down in the amory, just like the stirrup of a crossbow. There are only three arquebuses known to have survived with such a butt hole: two almost identical preserved at the Royal Armouries Leeds, both from the armory of the Dukes of Brunswick; the b/w photo I posted shows the somewhat earlier of them. Unfortunately there are no other photos around of this item. The barrel is of cast copper alloy ('bronze').
The third 'holed' arquebus, of almost identical shape and make, is in the Vienna amory, its lock parts (no plate) are modern replacements (illustrated below).
You are pefectly right, those holes seem to have disappeard by ca. 1500. They seem, however, had a temporary successor in the 1520's when an iron ring at the rear of the butt stock took over their function for a very short period of time - see attachment of a snap tinderlock arquebus from the Solothurn Armory, sold The Kuppelmayr Collection, Munich, 1896.
Interesting enough, the pan of the Royal Armouries arquebus never had a cover as there is no trace of a hole for the pivot, impractical though that must have been. In this aspect, the second arquebus is identical. I give a few images of it below, as I have done before.
As I have tried to show by various sources of illustration, the matchcord in these days is depicted held by hand or wound around the arm as it was only used to ignite the tiny piece of tinder used in the serpentine for actual ignition of the priming powder. So the match was not carried as an actual part of the gun.
As you seem to bear the same deep interest in these early guns as I do you really should read my older threads which hopefully reflect some essence of my intense studies in this topic for the past 30 years.
Best,
Michael