Though in fact, as readers, we didn't know that the symbiote went to Eddie Brock in issue #1... in that issue is where Peter thinks he got "rid" of the symbiote.
In Web of... #18 is the issue in which an unseen Eddie pushes Peter in front of a subway train, and makes another unseen appearance in Web of... #24 before finally appearing as Venom at the end of ASM #299.
It's in ASM #300 that we learn and "see" (via the flashback) that the symbiote did not indeed die and bonded with Eddie.
Web of... #38 comes out the same month as ASM #300, so over three years (our time as readers) had passed since Peter got rid of the symbiote.