That's a little misleading, because the line "expect to see this 1 in 33 runs" is still correct. You won't ever reach 100% as that requires literally infinite runs, and there's a chance it never drops after any finite number of runs. More correctly: 36.6% chance that it DOESN'T drop after 33 runs. In other words, 36.6% of guilds won't see it drop after 33 runs. Whereas 63.4% of guilds will see it drop once or more.

Also, your calculation doesn't account for multiple drops, which is where those "missing" percentages went. The chance of exactly 1 drop after 33 runs is only 37.4%. Meaning that the remaining 26% of guilds that did in fact see it drop, they had it drop more than once.

Chance of 1 drop in 33 runs: 0.03¹ * 0.97^{33 - 1} * (33 choose 1) = 37.4%

Chance of 2 drops in 33 runs: 0.03² * 0.97^{33 - 2} * (33 choose 2) = 18.5%

Chance of 3 drops in 33 runs: 0.03³ * 0.97^{33 - 3} * (33 choose 3) = 5.9%

If you multiply these and add them up, you will get 99% (3% times 33).

137.4% + 218.5% + 3*5.9% + ... = 99%