Differences training would not be required.
You did not say what aircraft you were flying before, but I'm assuming it was a PA28 or similar. With an SEP rating, you can happliy jump into any single engine piston aircraft for the first time, and fly it (withing your weight and other limitations). The "differences training" you did was a very sensilble option when flying a new aircraft for the first time, and may have been some club requirement for a new hirer, or insurance reasons, but other than that has no legal relevance.
Differences training is required for a type specified as very different from the rating you require. For example, Microlights, diesel aircraft, and tail wheel aircraft all have a legal requirement for you to complete differences training before you fly them. This is at the instructors discresion, and would usually be 3-4 hours depending on how experienced you are.
I believe any hour long flight with an instructor, or any skills test would be vaild for SEP revalidation by experience, provided the instructor notes it as such and signs it with his licence number in your logbook.