Ordinary zombies and zombie dogs haven't gone extinct because they're low-level and respawn quickly, unlike the first tier two-star Lickers. When Zhang Yanhang scanned Raccoon City, he couldn't find any trace of them.
Of course, it's possible that the Lickers that did respawn were hiding in more concealed corners, which is why Zhang Yanhang couldn't find them. Unlike the Lickers, which might have already started respawning, there were no signs of respawning for the first tier three-star Gamma Type Hunters and Beta-type Hunters.
As for the second order one-star Prototype Tyrant, it goes without saying that they have the highest level, and waiting for them to respawn could take ages.
Zhang Yanhang actually hoped that more monsters would respawn in Raccoon City because his demand for these monsters was truly very high.
First, he needed a large amount of the E-quality Talent "Slow Corrosion" to upgrade the S-quality Talent "Chunling Endless."