Just looking at the books I referenced in one of my earlier you can see that they are using 2 different sets of Ilokano. "Let's Speak Ilocano" uses a more modern version of Ilokano that is easier understood by those who have a greater exposure to Tagalog. Whereas "Ilocano: Ilocano-English..." reflects more of what is generally referred to as "deep" Ilokano or that found primarily in the Ilocos Region.
This difference can cause some trouble with a new Ilokano learner. So what one must do is determine with whom you plan on speaking. If it is family from Pangasinan or friends in Hawaii than the more modern will get you by just fine. If instead it is family in the mountains of Abra then it would be better to focus on "deep" Ilokano.
So what are these differences? Some are in pronunciation of letters, other are differences in complete words or phrases. Examples are:
Letter E- in deep Ilokano the letter "e" is pronounced deep in the throat. Giving it almost a deep "Uh" sound.
Letter K- I have found that my family tends to pronounce the letter K from the back of the throat to the point it almost becomes silent. Yet other Ilokanos that I know do not stress "K" this way. I suggest listening to those you are going to talk to and mimic their pronunciation.
As for words, there are too many to name. "Let's Speak Ilocano" translates the word "dadakkel" as "parents". To the average Ilokano speaker "dadakkel" translates to "really big." My family had never heard dadakkel used in reference to parents.
The main crux of this post was just to make you aware that there will be differences in Ilokano. From barangay to barangay, province to province the language will shift. It is my hope that these tips on here will help give you a better understanding of the language no matter where or with who you speak.