If you go to https://nwdb.info/ and look up the name of the item it will allow you to change the GS level to look to see if it gains a 4th perk when upgraded. Just move the slider to below 600 GS or above to see if it gains a perk. There are a couple of named items that don’t give 3rd perk.
The rule of thumb I use most the time is anything with of the in the name won’t get a 3rd perk but I always check on website before I spend umbral shards to be safe.
I belive “Named” items, in the Brimstone Patch, will actually have glowing names.
Neither of those items has a gemstone prefix like “Frozen” or “Abyssal”.
Neither of those items has a stat suffix like “of the Soldier” or “of the Artificer”.
Both of those items will upgrade to legendary.
I use NW database if it’s in question. However, it would be great to have an icon or something that shows it. Or maybe just drop as a leggo even if its under 600. I see they had datamined 590 leggos in the upcoming patch.
So still have to rely on nwdb to know, or just feeling judging from the good stats. I thought there’s something special written or shown on the object/description. Like @Olgit said above.
But good to know that they will make it different in Brimstone.
The reason why I double check is there is some named items that don’t get 3rd perk when upgrades. Plus I really enjoy the website.
there are named items that don’t upgrade to legendary like hill’s strength, still mountain, thunder’s charge, etc and also there’s dungeon specific drops like the garden’s amulet from genesis that doesn’t upgrade to legendary either
if you’re not sure just check nwdb
By FOURTH perk, do you include gemstone or exclude gemstone ?
Sorry, I should leave it at 3rd perk and not include the Gemstone in it. I will edit it and fix it so it doesn’t confuse. Thank you
One exception to part of Halcyon’s quick check: all of the tempestuous items from tempests heart quests show gem prefixes and stat suffixes, but can all be upgraded to legendary.
Can this be upgraded ??
I tried one and it failed, but it has chance to be Legendary or not ? Because I’ve seen a Legendary one.
If it can I will buy another one, if not then I wont bother.
It’s really weird and VERY annoying why wouldn’t they make an important item that they already put the effort to make it upgradeable known at first sight like with different color or someone mentioned it will glow in later Brimstone patch. Why not make it like that before, when they added upgradeable 590. 
Named items don’t roll random stats/attributes. So no it’s not a named item.
I see, so the Legendary version must drop as a 600 GS by default then.
this is what new world makes bad, alone that this topic exists makes it even worse
i realy dont know how many purps i already dismantled
and always have to check 3rd partie site doenst make it better,
just give items the legendary status(orange) but no they have to make it complicated
honestly very annoying
A la prochaine maj il sera écrit named sur l’item et un visuel les différenciera des items non nommés. C’est actuellement ainsi sur le PTR.
There are also armor with suffixes that do, like the Tempestuous chest rewards.
At one point they were going to have named items show the third perk that could be obtained at 600GS but then ninja removed it from patch notes.
It’s even more confusing because, as Trufitus stated above, corrupted dynasty enemy drops like the Hills Strength tower shield rolls random stats with no added perk on upgrade, but the item is classified as named. It shouldn’t be as it should have a name like “Spectral Hill’s Strength of the Soldier”
If the third perk that rolls is random, then upgrading it won’t make it legendary. There are quite a few “named-looking” items in this category, which is why it’s worth checking NWDB before upgrading (unless you have an excess of umbrals).
The Tempestuous stuff annoys me, there is no indication that it will gain a perk when raised to 600 and I didn’t realise until another player told me. Wouldn’t have even thought to look it up as it follows the pattern of non-named items (gem attribute prefix and stat suffix).
It isn’t that simple. Good luck upgrading “Still Mountain” or “Joyous River” to legendary. There are a decent number of items that have a ‘name’ that doesn’t include and prefix or suffix and still roll random perks.
When was this upgradeable 590 named gears added to the game ? Brimstone is said to be released on October 18 and will have glowing name for named gears.
Lets see how long they release a feature and FIX that feature. So when was it ?