According to Man and Machine (3E), deltaware implants are always custom built, and literally get wired as they are implanted "to ensure perfect compatibility and flawless construction". It goes on to say that secondhand deltaware is considered beta grade in its new host.
Also (at least as far as 3E went), removing a cybernetic implant from it's owner incurred automatic and permanent damage to the implant. It seems rather dubious that a corp would have an operative important enough to give delta grade implants to, but use a damaged implant. Would they try to pass it off onto a runner that managed to negotiate access to their facilities? Hmm...
I think that was kind of what I was poking at from the corp greed angle, I'd imagine reclaimed delta ware would be resold as beta ware, then. Also, if they did act upon that, wouldn't a corp want to research how to make the ware more durable for their agents, so that upon recycling it, it wouldn't necessarily degrade?
I don't think it degrades, but rather that it's been custom built and tuned for someone who is not the new recipient. If you want it to be delta grade, you need to put in the extra work (and cost) to tune it to the new recipient.
