It is harped that we deliver by address, not name. Forwarding and post-processing of first-attempt-as-addressed mail is a bonus service we provide. There is no service standard for the timeliness of forwards. We try to be as quick as we can, just to keep things moving along, but there is no strict, publicly advertised goal. There are typical or average turnarounds, but no guarantees. Delivery by name according to memory or case label is neither expected or required. Source of truth is the list of valid names in the box. At least that is how they handle the city side, and then slide it on to us. And even then, the names are just an aide to the carrier, and the carrier is afforded both discretion and leeway, as long as they cover their bases (hold it in office for verification, if it looks significant, for example).
For subs that are new to the route, and new in general especially, I insist they deliver by address, and don't worry about names. They are already confounded with enough new things to learn and remember that are actually somewhat important. If they are not correct about delivering mail that should be forwarded, it can be annoying to everyone including regular customer and supervisor, but those mail pieces typically come back with a flag standing at attention, and if they don't, well shucks, the sender and recipient should have communicated about the change of address, when it was really that important.
Experienced, seasoned subs, who do run the route frequently should have a good idea, but I won't ever expect them to be certain, except in the rarest of cases, and know it as well as the regular (some subs do know a route better than their regular, for reasons). For example, the first route I subbed on, was for my small-town, hometown, that I grew up in and my family still lived there. The regular lived nearby, but got the job through a district wide bid just a couple years prior. They knew quite a bit about a few people, but I could run the route in my sleep and if I had any major questions, I could get ahold of the customer or a close relative of theirs for quick and accurate verification.