That 100 estimate is kind of a fascinating thing. Although they would repeat the number, a lot of senior military and IC folks, when asked, will say they don't really know what there were supposedly 100 of/how "AQ fighters" was defined: Arab AQ fighters? Non-Afghan AQ fighters? https://twitter.com/CraigMWhitlock/status/1305876451812671488

Here are three comments different counterterrorism officials made to me about the longstanding "100 AQ in Afghanistan" (now supposedly 200) estimate for my Pech book: a senior CIA official, an Obama NSC CT official, and a senior JSOC officer https://twitter.com/CraigMWhitlock/status/1305876451812671488?s=20

A 2015 unclassified military report suggested that 100 was the number of AQ fighters (however defined) who stayed year-round in Kunar/Nuristan with Farouq al-Qahtani, and didn't count others who came into other eastern provinces for the warmer months.

These al-Qaida numbers are also only as good as USG's ability to accurately/consistently detect members of a clandestine group actively hiding from them in remote areas of rural Afghanistan: very bad then and still very bad now, that is. https://twitter.com/idreesali114/status/1305889062864158721?s=20

An example—a 2010 AQ tribute video to slain fighters named 3 Saudis who, acc. to their bios, had been fighting in Zabul/Paktika/Khost in 2006.

In 2006, US mil was only aware of AQ fighters in Kunar/Nuristan—which drove troop deployments, as this senior US commander recalled:

Abu Ikhlas al-Masri was a shiny object for US mil in Afg in 2002-7, drawing them deeper into Kunar.

But the very fact that he was so visible in HUMINT reporting should have been a red flag: he wasn't actually a key AQ figure. Those guys were staying farther below the radar.

Another Egyptian, Abu Ubaydah al-Masri, turns out to have been making visits into eastern Afg at the time. Unlike Abu Ikhlas, whose job was to liaise w/ Taliban, he was a senior AQ figure involved in overseas attack plots—& his OPSEC was therefore better & visits went undetected.

This is in hindsight (which still isn't 20/20 when it comes to Afg). But it's worth remembering that at the very time US mil was fruitlessly chasing Abu Ikhlas around eastern Afg, Osama bin Laden was talking about how AQ could deceive US in very much this way. Here's UBL in 2004: