Would you approve use of these PCBs??? Delamination issue

The fact that they delaminated in only a year calls into question the quality of the workmanship, regardless of the fact that they were in storage. Like you said, if they delaminate in storage they most certainly would delaminate in the field, and in a safety-critical application this is absolutely unacceptable. I would agree with John D that these should be scrapped (depending on the cost, you may be able to work out a partial refund from the supplier) and order new ones from a reputable source. Also, if you have any authority to do so, I recommend pushing a redesign to hatch the copper pours.

If the storage conditions were relatively benign (eg. not cycling back in forth between temperature extremes in an environmental chamber many times), looks like their process was defective, maybe improper process control in their lamination press. Which means that the entire panel that was in the press on that run would be scrap and maybe (probably) every panel made around that time.

Given the low cost of 4-layer boards, you should scrap them and move on. Even if it was not safety-critical the cost of field failures is too high.

There are hundreds of PCB suppliers in the SZ Bay area, you should be able to find a better one across the street.

Definitely toss them. 4 layer boards even made domestically are inexpensive these days.

FR-4 will absorb moisture, and when laminated at high temperature and pressure the moisture turns to steam and creates pockets in the epoxy/glass substrate. My bet is these were already delaminated when they shipped them.

If you are even considering using them, even if you have a few that do not look delaminated, I would bake them at 250 degrees F for a minimum of 4 hours. Then reinspect them.

If you run them through reflow or wave and there is moisture in them it can be very ugly.