Because we are talking about the law and how it pertains to changes in jurisdiction and representation I thought of an interesting example to share.
In the late 1960s or early 1970s a California water rights case wound its way through the courts.
An upstream land owner decided to divert the majority of a stream, that ran through his ranch, for his own use and allowed only a small amount of water to continue downstream. For those of you that don't know it, this is not legal under California Law. (I don't think it is legal in any state but I am not sure.)
The title to the upstream rancher's land had been in private hands for a very, very long time. His ranch was originally the property of Spain when they owned California. The Spanish government had issued a land grant to a private party sometime in the 1800s. Though California had passed from Spain to Mexico to the United States that ranch had remained in private hands the entire time, all the way until the case went to court in the 1970s.
When Spain titled that land in the 1800s their laws held that he who owned the land also owned the water, all of it.
The court found that the current owner's title was traceable all the way back to the original Spanish land grant. Because the current owner's title was in fact based on the legality of the original Spanish title, Spanish water right laws were controlling in this case.
This interpretation has stood.
To this day there are California ranches whose water rights are based not on current California state law or even federal law but on the Spanish laws that were on the books at the time of the original land grants.