There are several pieces of lead that indeed appear to have melted and re-hardened. I still have some questions I don't feel like I have answers to.
Let's suppose a bullet is leaving the muzzle with a molten lump of lead in the rear (military ammo being open at the base). The lead flies along with the copper until they hit something, at which time the copper would be stopped abruptly. If the lead is totally melted, it might splash out at that time. Would it stay together, or be sprayed out of the cup? If it stays in the cup, it would deform but fill the cup as much as possible before splashing or spraying out. I think if the lead remains molten for a half a second or so, it would be dispersed enough that you would not find any traces of it. There are circumstances under which the lead might not splash or spray, like if it penetrates an inch or two into a tree and the lead would stay in the "wound channel" in the tree.
But I have to say I remain unconvinced that you have demonstrated a significant amount of melting lead, and the actual scenario under which it might happen sounds pretty speculative. I know a significant amount of testing was done during WWII at Aberdeen Proving Grounds, where all manner of small arms were fired under various circumstances. I have read some of those reports, and don't remember ever seeing anything about lead cores melting. Maybe they saw it and didn't document it, but they sure documented other stuff that seemed to be of marginal importance to the subject of their tests.