Interested in thoughts on keeping the integrity of historical data

Just to be clear, I am not looking for an explanation of how relational
databases work in this question, I have been creating relational databases
for many years, please read closer.

I have a database that needs to store information as it was originally
entered. So, for example, normally I would enter client information (name,
address etc) in one table, and specific transaction information in another.
Reports would print out with the appropriate information for now. In the
future, let's say the clients address changes. When I go in and change the
clients address, I am actually changing it for historical purposed as well,
unintentionally of course, and this is usually acceptable. If for example I
need to keep the historical transaction intact as it was originally entered
(with the now old address), I would need to inactivate the old client
information and create basically a new client to store the new address. This
of course is difficult to get the user to do, they will just change the old
address to the new address.

One way to go about this is to force the user to create a new client by not
allowing edits or creating a routine that aids the user in the process.

Another way to go about this is to create what is really a flat file for all
the information that needs to be historically accurate. The client table thus
becomes more of an extended drop down menu for entering multiple values into
the main historical table. I really think this is the better way to go about
this. What do you think?

I am interested in additional thoughts on this, thank you in advance.