You ask if blistering is common...
The frustrating answer is: yes and no. Many different boats from the early 80's onwards have blistering, including (!) Ericsons.
It is common knowledge that boats going from salt to fresh water often blossom out in blisters. Some years ago this was noted in a PS owner survey. I found it to be true with our previous boat, but so far our '88 Ericson/Olson has not done this. No, I do not know why.
The evidence is annecdotal, but, to me, is convincing. The owner of the E26 is probably telling you the truth, in other words.
Have it surveyed. Shallow blisters are common on most boats built in the last two decades. As long as they do not go into the laminate, just grind 'em out and fill with a good quality filler (no "Bondo" or any similar product with clay filler...).
Best of luck,
Loren in Portland, OR