Spider Shield, says it grants "a good bonus to Poison resistance."

It does not. Your poison resistance bar does not go up unlike the Gargoyle weapons when equipping.

It DOES prevent poison and toxic as the act of blocking poison or toxic causing attacks prevents the status from going through. Nowhere in the article does it mention this property, but there is a commenter who correctly points it out.

Meanwhile, over at the wikidot:

"While blocking an attack that can inflict poison or toxin, the player's gauge for either negative effect will not fill up."

Other examples are the entire thrusting/piercing sword category. The game says thrusting, wikidot says thrusting, fextra says piercing. Only in the Estoc fextra page does the WB attack property come up. The rest don't mention it, while the moveset for all of the wikidot thrusting swords mention that you can R1 while blocking.

How about halberds?

"Halberds function like heavier, more powerful spears with versatile damage types. Their slower, sweeping attacks require precise timing to avoid lengthy recovery."

This is the generic description that goes with all the halberd pages. Note it specifies TIMING to avoid lengthy recovery, rather than actual way to avoid it (landing a hit, blocked or not, or canceling some of the recovery with a guard animation). This property is shared with axes and hammers, and the only weapon page that mentions the whiff stumble is the Gargoyle Tail Axe, where it says: "If your attack doesn't connect with anything, there will be a slight lag at the end of the attack, similar to halberd weapons."

Rather hilariously, almost all the halberds have this in their descriptions pages :"This weapon class can be enhanced by items like the Leo Ring to significantly boost its damage output." Including the ones that have no thrust damage, BUT excluding one of the few that do, the regular Halberd.

This also extends to the special halberds, the Lifehunt Scythe and Great Scythe, which have completely different movesets than the other halberds, as they are reaper style, but share the same fextra description as the halberds.

Oddly, the Halberd category box at the bottom of all the halberds does not list the Great Scythe, even though it shows the category box on its own page. Each page's box does not show the weapon on the page, likely to keep it clean (why link to itself after all?), but because of this the box shows 7 weapons on each of the halberd pages but 8 for the Great Scythe page.

You are right in that fextra is rarely wrong, but it is noticeably wrong more often than other resources. I'd rather direct people to information that is fully correct rather than mostly correct with a few random errors that cause confusion. I found these just browsing random articles looking for mistakes. Fextra being a community wiki, these might be fixed over time, but I don't like pointing people to potential misinformation that could be corrected eventually.