What clearly seems to have happened is that somewhere in the intervening five years, Lynn plain forgot that Vern and Alice even existed. This, as I said earlier when I talked about this issue, is owing to Lynn's inability to keep track of her stable of characters. Since she doesn't seem to know that she should keep notes on who lives where, her cursory look at the previous treasury seems to have lead her to the conclusion "HUM! Since these are two random old people who are referred to as grandparents, they must be John's parents."
Lynn believes this so firmly, she had their liography written in such a manner as to make it fit her new understanding of events. Simply put, it's as if Danny's parents never existed in the first place. This leaves us the problem of how to reconcile the presence of Danny's parents in 1983 and the Patterelders in the years that followed. The only thing that makes the remotest bit of sense is to assume that
a) Danny's parents died a few years after this.
b) the Patterelders showed up to provide Bev some emotional support.
c) they liked the place so much, they moved in.
It's like how Rod's folks moved to Corbeil to make sure Lynn's tendency towards dimwit negligence didn't result in grandchild existence failure.