He wasn't the last Envoy in the books. As mentioned in the comments, that was only the case in the series noted here: Altered Carbon, why is Kovacs the last Envoy?.
I went back and my actual confusion stemmed from this line:
Pretty soon they were going to know that the Envoy Corps was an empty
I think my memory of that warped it into they knew other Envoys couldn't help him cause there were no others. That was not the reason it was an empty threat.
Another gaff on my part of memory is that he was
the last Envoy left at Innenin.
Just not the last of anywhere. Too bad I don't have Envoy recall.