They did not produce 1600 / 1640 and 1651 with a plain round nose, the last stocks they did that way were the 640 / 1100 / 1000 and even the last 640 have the schnabel.
From 1953 they always were either with a Schnabel or with a plastic and later a rosewood end with a white spacer.
Except for the tip, it looks original.
It was common to remove a broken plastic tip or even to round up à schnabel even in the '80s... Especially on american models (like the 4000 /4100) as they are wider than the slim euro models fore ends (of the Std style). As for the finish, tgis type of finish is easy to reproduce for a professional stock fitter...
There was a lot of aftermarket parts sold through HVA though an d they even produced special replacement stocks (I'll post a replacement stock for a 640 later).
If the sling swivels are 3/4" then the rifle is a recent import and it may have gone through the HVA custom shop, but if it bares 1" swivels, then it's most likely a modified stock (as per Tradewind and even more Ruko weren't much interested on aftermarket parts other than direct replacement).
Anyhow, these rifles have seen 40 + years of handling and this does not really play with the value of the rifle as per most of these rifles are not intended to be collectors but rather usual hunting rifles and people buy them for that, usually not for being a safe queen.
Anyhow, from what I see, for me, the tip seems to have been rounded. But who knows, it may also be a custom replacement. But the this type of stock is not in period catalogs and it's not in the HVA - Tradewinds litterature neither (and THE book claims three 1651 models, one with a schable and two with plastic / rosewood tip).
The 1651 Special and Lyx both had as a standard the ajustable trigger and the recoil pas from factory. Both have the plastic / rosewood tips.
The 1651 was the plainer version and usually was with a straight comb.
The fact the stock is unusual for both styles is the reason why I do not exclude a custom (replacement) stock.
But except a collector, who really cares those details ??